Descriptions of Twenty-Eight New Species of Acephala and One Gasteropod, from the Cretaceous Formations of Nebraska Territory

1856.]

Anodonta WaMamatsnsis,^{Lea. Tr.}

Am.

P.S.v. _6,p. 78.=.4.iriangulata,Trask.

A.roliindovata,Trask.

From Sacramento

River.

Anodonta angulata. Lea. ^Tr.

Am.

P. S. v. _6,p.97.=.4. _feminalis, Gould.

A.

Randall), Trask.

From

_upper

San

_Joaquin.

HelixOreffonensis,Lea. Trans.

Am.

P.S. v.6,p.100. Point_Cypress,Monterey County.

Jlelix Nickliniana, Lea. Trans.

Am.

P.S.v. 6,p. 100.

Tomales Bay ^and

,

Deadman's

Island.

Helix CaUforniensis, Lea. Trans.

Am.

P. S. v. _6, p.99. Point _Cypress, Monterey County.

Lt/mneeaexigua,Lea. Trans.

Am.

P.S. t._9,obs.v. 3.

San

Antonio Arroya.

Lt/mnceapallida,

Adams.

Journal BostonNat.Hist.See.v.3.

San

Antonio Arroj'a.

Physa

heterosfropha, Say. Nicholson'sEncy.

Am.

Edition. Los Angeles.

Melania_occata, Hinds. Voy.^{of the}Sulphur,pi. 15,^{f. 5.}

Sacramento

River.

3Ielania

scminalis, (Faludina, Hinds.) Voy. Sulphur, pi. 16,fig. 22. Sacra-

mento

River.

Planorbis _(rivoli.s, Say. Nicholson's Ency.

Am.

Ed.

Hern

Lake. _Slightly variesfrom theMichigan specimens.

Planorbis

ammon,

^{Gould. Proc.BostonSoc. Nat.Hist. v.} 5,p.129. Lagoons,

Sacramento

_Valley.

Descriptionsoftwenty-eight new _{species of}AcephaJa

and

one Gasteropod,

from

^the Cretaceous formations ofNebraskaTerritory.

By

^F.B.

Meek and

F.V.

Hayden,

^M.D.

Pholadomya

undata. Shell oval or ovate, moderately ventricose, anterior end rounded,posterior extremity

rounded

_chieflyfrom below, ^cardinal border nearly straight;base

somewhat

broadly curved;beaksrather elevated, incurved, placed

between

the centre

and

the anterior end; surface (of cast)

ornamented by

numerous,regular, distinct, concentric undulations,

which

are crossed

by much

smaller _{radiating costse,scarcely}

marked

in the depressions between.

Length

^{about oneinch.}

As we

havenot seen thehinge^ofthis species,

we

referitwith doubttothe above_genus.

The

_radiatingcostajare about_{equal, thespaces}between,

and

in consequence^of being

marked

_{only on}the concentric undulations,

and

not in the intermediate depressions, furnish a character

by which

^even fragments

of

the species

may

^{be atonce}identified.

Localityand_position.

Mouth

ofJudith _River,inasandstone supposed^tobe

same

asNo. 1of theseries.

GoNiOMYA

AMERICANA.

Our

_Specimensofthisinteresting^shell aretooimper- fect togive a clear idea of^itsform,

though

the direction of the linesof

growth

indicatean oblong^orvery

narrow

oval_outline,withanarrowly

rounded

ante- riorand subtruncate_posterior. Laterally the valves

must

have been considerably compressed.

The

beaks_{are small,}not

much

_elevated,

and

_placedin

advance

of the centre.

On

the

two

extremitiesthe_costse,

which

_{are quite}distinct, tra- versetheshell obliquely

backwards

from nearthehinge^tothe base,whilethose originating immediately^{in front}

and

behindthe beaks, converge

and meet

at various distances

down

the sidesof the _shell, soastoform arched orconvex angles offrom 20 to

30.

Surface

ornamented

bj'fineirregular^lines ofgrowth, crossed

by

regular, equi-distant, radiatingrowsofminutetransparent granules, placed at regular distancesfrom each other. These granules^{are so}smallas to be_scarcelyvisiblewithoutthe aidofastrongmagnifier,under

which

_{they look}

likeminute drops^ofmelted amber.

In its surface markings ^this species resembles G.Dubois of Prof. Agassiz, (^Eludes critiques sur lesMoliusquesfossiles, tab. _1.)but inour _species the con- verging^costa; continueto

meet

atthe

same

acute _{angles as}farasthey can be traced towardsthe points of the beaks,while

on

the beaksof G.Dubois

and

[April,

other.allied species,these angles are truacated,

and

the opposite ^costaeunited

by

horizontal bars. Perfect specimens

would

_probablyshovrotherdifferences.

Thisis,

we

_believe,the firstspecies of^thisgenus foundⁱⁿAmerica. According toProf.Bvonn,(IndexPalaion(olofficus,) five specieshave beenhitherto described fromthewholecretaceous _sj^stem,

two

of

which

were from theNeocomien,

two

from thegreensand,

and

onefromthe true chalk.

Localityand_position.

Moreau

_TradingPost,No.5oftheseries.

SoLENSUBPLICATUS. Shellvery^thin

and

_fragile,elongated, cardinal

and

basal margins straight and _parallel; buccal extremity obliquely truncate, anal end

rounded

from _below,both ends gaping; beaks_nearlyatthe anterior extremity, notdistinctfrom nor_risingabovethehinge^{line. Sixto}eightbroadly rounded, very^faint plications radiate from behindthe beaks_obliquely

backwards

tothe posteriormargin,^to

which

_{they appear}tohave imparted^aslightly

waved

out- line

; surface

marked

withfaint linesof growth, and minutetransverse closely arranged striae,

which

do notradiate from _{the beaks,}but traverse theshell at rightangles^toitslongitudinal diameter. Length^1-15inches;breadth-26inch

;

heiglit '42inch.

The

finetransverse striaeonthisshellareonly^visibleunderahigh magnify- ingpower,

and

appear^to havebeenas well

marked

onthe inside asonthe ex- terior,distinct impressions of

them

_beinglefton internal cast.

Locality^aiidposition.

Moreau

_river,No. 5oftheseries.

Tellina gracilis. Shell elliptical, moderately compressed, extremely ^thin

and

_fragile;buccal margin rounded^;posteriorendcontracted, subtruncate,

and

having^a broadobsolete ridge passing from^thebeaks _obliquely

backwards

to the postero-basalmargin; cardinal border convexbefore

and

concave behind thebeaks; lower border forminga regular elliptical curve

; beaks rather de- pressed,

and

located alittlebehind the centre; surface

marked

withfine lines ofgrowth.

Length

^{-90inch;breadthofleftvalve-ITinch;}height^-60inch.

The

abovedescription^is

made

outfrom_{a single}leftvalve, soattachedtothe matrixasto

show

only external characters.

Localityand_position.

Mouth

of the Judith, ⁱⁿasandstone supposed^tobethe

same

as No.1of theseries.

Tellina eqoilateralis. Shell elliptical, compressed, moderately ^thick,ex- tremitiesrounded;anteriorend_slightlybroader thanthe posterior;beaks_small, notelevated, located a^littleinadvanceof themiddle;surface

marked

withfine 'regular concentric^lines. Length of right valve 1-15 inches; breadth-12 inch

;

height^{"57 inch.}

We

haveofthis species but one _right valve,

showing

^{noneof its internal} characters.

The

position of ^itsbeaks, as well asits

much

_{greater thickness,} preclude^{theidea ofits}being anopposite valve of the^last.

Localityand_position.

Same

as preceding.

Tellina? Cheyenensis. Shell ovate,compressed, very^thin; anterior extre- mity rounded; posterior end subtruncate or rounded from _above,

and

_very obtusely angular below; base forming an _elliptic curve; beaks

somewhat

elevated,placed^alittlein advanceofthe middle, surface

ornamented

with fine Huesofgrowth

and numerous

small regular concentric wrinkles,

becoming

^mere

linesnearthebeaks

and

onthe extremities. Length^-88inch;breadth -36inch;

height^{-61 inch.}

We

have only seen the outside of^thisspecimen.

Localityand_position. Forksof

Cheyenne

River, No. 4 of theseries.

Tellina scitdla. Shell elliptical,small,thin,

much

compressed, curved ^so as tobeconvex on theleft,

and

_slightlyconcave on_{the right}sides

; extremities narrowly rounded,the anteriorend being wider thanthe posterior; beaks_small, nearly central^; base forming ^a regular elliptic curve

; surface polished,

and marked

withdistinct linesofgrowth. Length^-50inch;breadth-13inch

; height 30inch.

Localityand_position.

Moreau

_River,No. 5ofseries.

1856.]

Tellisasubelliptica. Shell small, ovate orelliptical,thin,

mnch

_compressed;

anterior extremity rounded; posteriorend

somewhat rounded

orsubtruncate_; beaks _{small, not}

much

elevated, a^littleinadvanceof the centre;^surface'rather faintly

marked

with finelinesofgrowth.

Length

^-50inch; breadth-12inch;

height^-32inch.

This_speciesischieflydistinguishedfromthelast

by

^its

more

_broadly

rounded

extremities,^lessdistinctlinesofgrowth,

and

greater thickness.

Localityand_position. CherryCreek,

Upper

part ofNo. 5oftheseries.

Tellina PttOUTt. Shell ovate,

much

compressed, very^thin

and

_fragile; ex- tremities

rounded

^: _posterior cnu

somewhat

contracted,

and

_{having a broad,} indistinct ridge passing from the beaks _obliquely

backwards

to the postero- inferior margin, ^{the outline of}

which

it

may

^have slightlymodified; cardinal borderconvex_before,

and

concave behindthe beaks

;

umbones

_{nearlycentral,} elevated,

somewhat

_{gibbous,closely}approximate^;surface

ornamented

withfine butdistinct linesof

growth

^{; internal laminaj of theshell}

marked

with _faint, very^fineradiating^lines;sinus of the palleal impressionoblong,obtuse orsub- truncateatthe extremity,aboutone-third the length of the^shell.

Length

^2*42 inches; breadth -83inch; height1-GO inches.

We

have not seen thehinge^ofthis shell.

The

_speciesisdedicatedtoDr. H.

A._{Prout, of} St.Louis, Missouri, to

whom we

are indebted for the onlyspeci-

men we

haveseen.

Localityand_position. Fort Benton, No.^{4 of theseries,}

Cytherea

Deweyi. Shellsubcircular or slightlyoval,

somewhat

compressed;

beaks moderatelyelevated, a^littleinadvanceof thecentre;surface

ornamented by

^distinct irregular ^lines of

growth

;lunule small,narrow, ^{oval or}broad lan- ceolate, notverydistinctlyimpressed; muscular impressions shallow, anterior one

narrow

ovate; posterior broad _{ovate,acutely}angular above; palleal im- pressionhaving^{a rather}deeptriangular sinus,forming^attheajiexan angle^of

55;

^{bordersmooth.}

Length

^-96inch;breadth-51 inch;height^"85inch.

Specimens slightly

more

_elongated,but apparently^identicalwith _this, occur onthe Yellow-stone Riverin abed

we

have consideredthe upperpart ofNo._4, but

which may

represent No. 5. This _species is dedicated to Prof.Chester

Dewey,

^ofRochesterUniversity, N. Y.

Locality

and

_position.

Moreau

_River,No.5of the series.

Cytherea

Nebrascensis. Shell subcircular,

much

_compressed;beaks

somewhat

elevated, small, a^{little in} advanceof the centre; ligamentarycavitylong

and

very

narrow

lanceolate;surface

marked

withratherfaint linesofgrowth.

Length

VO inch;breadth-28inch;height^{-GO inch.}

The much more

compressed form^{of this shellwill serveto}distinguish ^itat once fromthelast.

Localityand_position.

Same

as preceding.

CoRBULA

VE?iTRicosA. Shell Small,very thin, subglobose,nearly equivalve^; anterior end broadly

rounded

; posterior extremity abruptly contracted ^{into a}

narrow

prolongation; beaks elevated, ventricose, a^little behind the centre of the globose part of the shell; surface

marked

with distinct irregular ^lines of

growth

^; cardinal tooth of rightvalve prominent,^flattened; posteriormuscular impressiondeep^; pallealimpression having^abroad triangular sinus.

Length

55 inch;breadth-26inch;height^-27inch.

Localityand_position.

Same

aslast.

CoRBULA

MoREAUENSis. Shell Small, subovate,ventricose,

rounded

in front, suddenly^contracted

and somewhat

attenuatebehind;beaks prominent,^situated behindthemiddle of thebroadestpart of theshell,rather inclined

backwards

;

surface

ornamented

with_strong,regular, elevated concentriclines,nearly equal- ling thespacesbetween.

Length

^{about-27inch; breadth-10inch}; height^'16 inch.

We

have not_yetseentheleftvalveof this shell,northe interior of the_right,

[April,

from which the above description ^is

made

out.

The

_species

may

be distin- guished fromthehistby^its

much

_stronger

and more

regular concentric^lines.

Localityand_position.

Same

aslast.

CoRBULA?

GREGARiA. Shell Very small,

somewhat

triangular, subglobose^; right valve

more

ventricosethantheleft

;beaks_{nearly central,}gibbous, that of the_I'ightvalve elevated considerably above^theleft,incurved;surfiicepolished

and marked

withafew_{faint,irregular,}concentric _Avrinkles, indicating stages ofgrowth;hinge having under^thebeaks_{a single}prominent^toothineachvalve;

anteriormuscular attachment indistinct,posterior raised upon a strongly pro- jectinglamina; pallealimpressions scarcely sinuous.

Length

^-13inch;breadth

10 inch;lieight -13inch.

Itiswith

much

doubt

we

refer thislittleshell to thegenus ^{Corbvla. In the} inequality of^itsvalves, as well asinthe character of its hinge, ^itagrees ex- actlywiththat genus, but

we

have seennospecies of Corhula having^eitherof themuscular attachments raised

upon

a projecting plate, asinthis shell. In thisrespect^itis

more

like CordillaofDeshays, but^itappears^to

want

thespoon shapedprojection of thehinge^{of that}genus;

and

itisthe posterior, instead of the anterior muscular attachmentthat hereformsa projectingplate.

We

sus pect^itbelongs^toan undescribed_genus.

Localityand_position. Yellow-stone_River,one

hundred and

_fiftymilesfrom mouth,

where

itisfoundinvast

numbers

_{compactedtogether}inconcretions,ⁱⁿ theupperpart of No. 4 of theseries.

AsTARTE

GREGARIA. Shell Small, subtriangular,rounded below

and

at the extremities, nearlyequilateral,valvesmoderately convex;beaks

much

_elevated,

rather pointed, incurved, approximate, slightly turned forward

; escutcheon

narrow

lanceolate; lunule

somewhat

_broadly lanceolate or

narrow

_ovate, not verydistinctlyimpressed; surface

ornamented by

small,but distinct con- centric undulations,

and much

finer linesof

growth

; bordersmooth; muscular impressions shallow. Length^{-21 inch};breadth -14inch

;height^{-21 inch.}

Localityand_position. Yellowstone River, fromabed probably near the top of No._4,ifnotinNo.5of the series.

Abundant.

NocDLA

sciTULA. Shell ovate, rather ventricose,rounded_{in front,}

somewhat

contracted

and

_narrowly

rounded

behind;

umboual

_{region gibbous}

; beaks prominent,incurved,approximate,^{located in} advance of the middle

; surface

marked

with _{distinctly elevated,}regular concentric lines, about _equal to the spacesbetween,

and

_strongeronthemiddlethan towardsthe extremities of the valves; dorsal border

marked by

^{a distinct} longitudinal groove behind ^the beaks. Length^-39inch;breadth-21 inch;height^{-22 inch.}

From

N.ventricosaofHall

and

_{Meek, (see}vol._5,

new

_series.Trans.

Am.

Acad.

Arts and _Sciences,)to

which

it bears

some

resemblance,^this

may

^{be distin-} guished

by

^itsbeaks being^located nearerthe anterior end,

and by

^itslarger size

and

comparativelysmaller concentriclines.

Localityand_position.

Moreau

River, No. 5 of the^series.

Ndcdla

Evansi. Shell elongate,narrowelliptical,thin,moderately convex;

cardinalmarginnearlystraight,

marked

withadistinct longitudinal groove on eachvalve

;extremitiesrounded,posteriorend compressed and slightlygaping;

inferior border forming an elliptical curve,with sometimesafiiint impression near the middle; beaks verysmall, not

much

elevated, locatedinadvanceof the centre; surface polishedand

marked

withfaint lines of

growth

; muscular impressions indistinct;teeth ofthehinge numerous,closely interlocked.

Length

72 inch;breadth-22 inch; height^{-32 inch.}

DedicatedtoDr.

John

_Evans, U.S. Geologist of

Oregon

Territory.

Localityand_position.

Moreau

_River,No.5 of theseries.

NucuLA

EQuiLATERALis.

Our

_Specimens ofthis shell are only ^casts.

The

species

may

^becharacterized as follows: subelliptical,ratherconvex; extremi- tiesnarrowly rounded;beaks_central,

somewhat

elevated;

umbonal

region gib- bous; muscularimpressions comparativelylarge, distinct, butnotdeep; border

1856.]

smooth

;teethof the_hingjenumerous,short,obtuse, closely interlocking.

Length

64 inch;breadth -21 inch;height ^-25inch.

Even

castsofthisspecies maj-always be

known

fromthe _last,by^thecentral position of thebeaks

and more

_narrowly

rounded

extremities.

Locality

and

_position.

Same

aslast.

Nucni-A SUBPLANA. Shell small, oral, compressed^{; anterior} end _obliquely subtruncate from the beaksalittle

more

than half

way down;

posteriorond round, base broadly

rounded

; beaks prominent, compressed,^locatedabouthalf

way

^betweenthe centre

and

the anterior end; surface (of cast) having^afew faint indications of concentric undulations; teeth ofhinge moderately long;

border smooth. Length^-25inch;breadth-09inch

; height ^-20inch.

Of

this little

Nucula we

have _{only seen}casts. It

may

^be

known

fromother speciesfromtheseformations

by

^itsshortcompressed form

and

elevatedbeaks.

It israre.

Locality

and

_position. Yellow-stone_River, one

hundred and

fiftymilesabove mouth, ^inabed supposed^tobe upperpart ofNo. 4ofseries.

NuccLA

CANCELLATA. Shell rather large

and

thick, ovate or subtriangular, ventricose, pearlywithin

; anteriorend short, obliquely truncate, posteriorend longer, narrowly

rounded

;

umbonal

_{regiongibbous}; beaks

somewhat

_elevated, slightlyincurved

; escutcheonlanceolate; lunule ovate, flattened,but_scarcely impressed; surface

ornamented by numerous

flatlj^rounded,simple, closely ar- ranged, radiating costs,

which

are crossed

by

small, irregular, concentric wrinkles,

and

finerindistinctlinesof

growth

; borderneatly crenulated.

Length

93 inch;breadth-50 inch

;height^{-65 inch}

Thisbeautiful

Nucula

resemblesin itssurface markings N.pectenata of

Sow-

erby, (Min.Conch,vol. _2,page 209,fig. 6,V,)butdiffersinthe form

and

_depth ofitslunule,

which

israther

narrow

ovate

and

_ver}'shallow,while inSowerby's species^itisdistinctly cordate

and

deeply impressed.

The

muscularimpressions,

though

large,are

much more

shallowthaninN._pectenata.

The

_radiatingcosteeof our_species

become

obsolete onthe lunule

and

escutcheon,

and

areaboutfive timesasbroadas thegroovesbetween, nearthe border.

The

anteriormuscular impression^isbordered

by

a distinct ridge,

which

extends_nearly

up

^{tothe beaks.}

'

Locality

and

_position.

Moreau

_River,No. 5of theseries.

Nucula

planomarginata. Shell ovate,

somewhat

compressed,pearlywithin;

anterior end very short, obliquely truncate; posterior end long

and

_narrowly rounded, dorsal

and

ventralmarginsforming,fromthebeaks backwards,ellip- ticalcurves; beaks

much

elevated; surface

unknown

; muscular impressions faint

;border smooth.

Length

^-95inch;height ^{GO inch};breadth-26inch.

We

have only seen internal casts of ^this species,theshell being always^left adhering^tothe matrix,from

which we

inferthe surface

was

_ornatelymarked.

It

may

^beatoncedistinguished fromthelast

by

^its

more

compressed form

and smooth

border.

Locality

and

_position.

Same

aslast.

Pectcnculina parvula. Shell very small, obliquely oval,

somewhat com-

pressed, inequilateral; buccalend

and

base

rounded

; anal extremity

rounded and

_slightlyextended_obliquely

downwards

; cardinalborder_short,

and

_having anarrow,well defined, longitudinally^striate areaon eachvalve; beaks_small, not

much

_elevated, about

midway

^{between the centre}

^and

^{the anterior end;}

surface polished

and marked

withlines of growth, sometimes ^crossed

by

^faint indications of radiating^costae; hinge havingⁱⁿeach valve three or four teeth on each side of the central triangular ligamentarypit; interior

marked

with faintradiatinggrooves terminatingin distinctcrenulationsatthe border.

Length

18 inch;breadth -10inch

; height IS inch.

This little shell might,

upon

^ahasty examination, be mistaken ^for Cardium varum, (Evans

and Shumards

unpublished MS.), butitpossesses ^all thecha- racters of theabove _genus.

The

shellisoften so translucent that the internal radiatinggrooves^{are seen}through^it.

Locality

and

_position. Yellow-stone_River,No. 5of theseries.

[April, Arca

(cucull/Ea) cordata. Shell thick

and

_{strong, subovate,}

somewhat

triangular or cordiform, very ventricose, abruptly rounded before, obliquely subtruncate_behind,and forming^abroad curve below; uniboncsgibbous,

much

elevated, incurved, located nearthe anteriorend; ligamentary^areaveryshort, deeplyexcavated,grooved and finely striated longitudinally^; surface

marked

with_strongimbricating^linesofgrowth andindistinct radiating^costffi. Length 2-03 inches; breadth1-77inches; height^{1-9G inches.}

Length

^ofligamentary area1-25 inches;breadthofdo. -30inches.

This species, in ^its thickness

and

_general appearance, approaches ^Cucullcea Ifebrascensis,(Owen,) but

may

be distinguished by^itsshorterbuccal_extremity,

more

elevated, approximate and incurved _beaks,

and

_{especially by}its

much

shorter

and

narrower ligamentary^area. There is in our specimen^{a distinct} sulcus starting from before the beak of each_valve,

and

_{extending obliquely}

downwards

toa point a^little behind themiddleof the_shell,

where

itdies out beforereaching^{the border.}

When

viewed on either end,^thisshellpresents a beautifulcordate form.

Localityand_position.

Moreau

_TradingPost,No. 5ofseries.

Arca

(cucdll/Ea) Shumardi. Shell _oval, ovate,

somewhat

_globose, rather thin,obliquelysubtruncate_behind,rounded_before,

and

_{forming anelliptic}curve

below

;

umbones

_{very gibbous, oblique, moderately elevated, incurved,}

and

located alittleinadvanceofthecentre;surfaceornamented

by

^{distinctlinesof} growth,^crossed

by

numerous,^{rather indistinct} radiating ^costaj; ligamentary area _straight, narrow, moderately excavated, grooved

and

striated longitu- dinalljr;hingehavingⁱⁿeachvalve three or four transverselystriated,oblique, lateralteethon each _side,

and

_{small,irregular,}intermediate transverseonesin the centre;border smooth. Length (specimen about four times the

medium

size) 1'67 inches;breadth 1-28inches; height ^1-40inches.

Thisis oneof themost

abundant

andbeautiful bivalvesfoundinthe creta- ceous rocks of theupperMissouri country. ^Itvaries

much

inform,

some

ofthe specimens being

more

_{nearly of}anovate form,ⁱⁿconsequence^ofthe anal region beingextended,

and

thebeaks

more

_oblique, whileothers are shorter

and more

rotund. These

two

formsare quite well

enough marked

^{toconstitutea}specific distinction,^ifthey were^notconnected by

numerous

intermediate ones.

As

these differencesarenotdue toage^orsize,

we

are inclinedtoregard

them

as sexual.

In oldshells the radiating ^costas are usually obsolete. In

some

specimens a single raised ^line maj'beseen passing from behind^thebeakof the rightvalve tothe posterior border, following the direction of the raisededge^ofthe poste- riormuscular impression. This israrely seen ontheleftvalve.

We

dedicate the species^toDr.B. F.

Shumard,

^ofSt.Louis, Missouri.

Localityand_position.

Same

aslast.

Mytilus attexuatus. Shell

much

_{elongated, slightly} arcuate; extremities compressed and rounded;anteriorend

narrow

;beaksnearly terminal^; surface (ofcast) faintly

marked

withlinesofgrowth.

Length

^{1-90inches;breadth -50} inch;height^-50inch.

From

M. Galpiniamts

and

M._Meckii,(Evans

and

_Shumard,)thisspecies

may

be

known _by

its

much

_greater proportional length andless gibbous ^beaks.

Having

only seencasts,

we know

_nothingofitssurfacemarkings.

Locality

and

_position.

Same

aslast.

Aaicula?

fibrosa. Shell ovate, subtriangular,very oblique,pointed ^{at the} beaks,

somewhat

rounded below; beakssmall,acute, placed^atthe anterior ex- tremity,

and

scarcely rising above the hinge; right

and

leftvalves_alike,con- vexlyarched from the beakstothe base

; posterior

wing somewhat

^flattened

and

_apparentlybroadly rounded; surAxceornamented bystrong,rounded, ^radi- ating plications,

which

bifurcate very irregularly,

and

are crossed _bj'strong concentric undulations, so as^togive the surface,

which

isotherwise smooth,^a subnodose appearance.

Some

ofour specimens

must

have beenas

much

as

two

inchesinlength

when

_perfect.

1856.]

It iswith

much

doubt

we

_placethis shell intheabove _{genus, as}

we

havein

none

of our specimens ^seen

any

indications ofan anterior wing. ^{It is also}

worthy

^of note, that the substanceof the shell is

composed

^{of an internal} lamellar,

and

anexternal fibrous portion, ^like Finna,from which, however,^it differs inhavinga posteriorwing-like expansion.

The

_radiatingcostaearefaint orwanting on^thewing.

Locality

and

_position. Forksof

Cheyenne

River,No.4 ofseries.

Inoceramus ventricosus. Shell ovate, oval or oblong, extremely inflated, very^thin

and

_fragile,structure entirely fibrous;cardinalborder_straight

;ante- riorend rounded,posterior end apparently' subtruncate,base broadly curved;

umbonal

_region remarkably gibbous^; beaks oblique, located ^at the anterior extremity; surface

marked

withfineregular imbricating ^linesof growth,

and

occasionallywithafewfaint irregular con'entric undulations.

Length

^about 4-30inches;breadth(of right valve) I'TO inches^; height2-T5 inches. Thickness of thickest part ofshell,near_{the hinge,}-12inch;do.ofthinnest partnearborder

03 ofaninch.

The

moststriking characteristics of^thisspecies are^itsremarkably^ventricose form, extremethinness

and

entirely fibrous structure, there being no ^internal lamellar portion, as ^isgenerally the case ^{in this} genus. Inour specimens ^the calcareous matter has been replaced

by

ferruginous

and

silicious matter, so astopreserve the original structure of theshell perfectly. Iftheleftvalveisas gibbous^astheright,thetransversediameterof the shell

must

be considerably greaterthanitsheight.

The beak

ofoneofour specimens appears^tohavebeen truncated.

We

_{have only}seen right valves.

Locality

and

_position.

Mouth

ofJudith_River,in sandstone,supposed^tobethe

same

asNo. 1of theseries.

Pecten

Nebrascensi.s. Superiorvalve suborbicular,moderately compressed,

ornamented by

^{twelve to fifteen} strongly elevated costae about equal ^{to the} spaces between;surface

marked

_{with very}fine,closelyarranged^concentriclines, crossed

by

equally^fine

crowded

_radiatingstriie

; buccal ear (imperfectⁱⁿour specimens) apparentlytriangular, rather distinctly

marked

with_{radiating costae,} crossed

by

^{concentric striie}strongerthan onthe

body

^{of th valve}; aunalear smaller, triangular,concave onthemargin,

and marked

withdistinct concen- tric lines.

Length and

^{breadth-49inch.}

From

F. venustus of Dr.Morton,(Synopsis,pi. 5, fig.5,)to

which

thisspecies appears^to be_{closelyallied,}it

may

^bedistinguishedby^{the fine}radiating ^striae.

In

some

ofthe specimens ^thecostaj occasionally bifurcate,whilethe radiating strife never run exactly parallel ^to the _costae, but _pass veryobliquelyalong theirsides. Thesestriaeare sofineastobeinvisiblewithoutthe aid of alens.

We

have not seen the inferior valve.

Locality

and

_position. Yellow-stone_River, one

hundred and

_fiftymilesfrom

its

mouth,

^inabed supposed^torepresentNo. 5oftheseries.

Natica subcrassa. Sh^ll obliquely oval or oblong, thick;spire rather short;

volutions threetothree

and

a_half,convex;suture distinct or

somewhat

_grooved;

surface

marked

with_stronglinesofgrowth,

which

rise,onthe

body

whorl, into distinct imbricating wrinkles; outer _lipbevelled; inner _liprather thick,

and

nearly covering^{the small} umbilicus

; aperture ovate, oval,orelliptical,nearly as obtusely

rounded

aboveasbelow.

Length

^{-95inch;breadth-87inch;}apical angle about

93.

It ispossible there

may

^{have been} other surface markings than^those

men-

tioned above,^asallour specimens^{are so}

worn

that finelines

would

havebeen obliterated,

had

_they existed.

The

_species

may

^be

known

from those found in thehigher

members

oftheseriesinthisregion,

by

^itsstronger^linesofgrowth,

and

greater thickness.

Locality^aiidposition.

Mouth

of Judith _River,from asandstone supposed^to bethe

same

asNo.1 of the _series,

where

it is associated with Tellinagracilis,

and

T.

equilateralis.