BRACHIOPODA SYSTEMATICS

Suborder Dalmanelloidea Moore

1952

Family RHIPIDOMELLIDAE

Schuchert 1913

Genus

RHIPIDOMELLA

Oehlert, 1890

RHIPIDOMELLA

cf. R.

MISSOURIENSIS

(Swallow), i860 Plate 3,A, figures 1-3

i860. Orthis missoimensis Swallow, Trans. St. Louis Acad. Sci., vol. i, pp.

639-640.

1914. Rhipidomella missouriensis Weller, Geol. Surv. Illinois, Monogr. i, pp.

148-149, ^pi. 20, figs. 1-8.

Weller's subdivision of the Mississippian Rhipidomella is based chiefly

on

internal features,butto

some

extent

on

theexteriors.

Three

of the species he recognized, R. missouriensis (Swallow),

R. oweni

Hall

and

Clarke,

and

R. hurlingtonerisis (Hall), resemble each other verycloselyexternally

and

requireconfirmationof interior details for accurate specific designation.

The Represo

collection contains only a single complete specimen

and

fragments of

two

others,

none

of

which

reveals internal characteristics.

On

the basis of size

and

shape the species appearsclosest to R. missouriensis.

Figured

specimen.

— ^U.S.N.M.

^127910.

Genus

PERDITOCARDINIA

Schuchert and Cooper, 1931

PERDITOCARDINIA

^cf. P.

DUBIA

(Hall), 1857 Plate 3,B, figures 4-7

1857b.OrthisdubiaHall, Trans.Albany Inst., vol. 4, p. 12.

1914. Rhipidomelladubia Weller, Geol. Surv. Illinois, Monogr. i, pp. 160-161, pi. 83, figs. 9-10.

NO. 3 MISSISSIPPIAN

FAUNA, SONORA — ^EASTON

^{ET AL.}

43

1932. Rhipidomella (Perditocardinia) dtibia, Schuchert and Cooper,

Mem.

Peabody Mus. Nat. Hist., vol. _4, pt. i, p. 135, ^pi. 19, figs. 12, 16-17, 20-22.

Examples

of shellsclosely resembling Hall's species are present in this collection

and come from

the

Venada

limestone in the small hill

i^ ^miles west of Bisani.

The

beds containing P. dubia are

younger

than the

Chouteau

because Hall's species ranges

from

the

Warsaw

to the Ste. Genevievehorizons, so far asispresently

known, and

bothof these overlie the

Chouteau

equivalents in the Mississippi Valley sections.

Figured

specimens.

— ^U.S.N.M.

^{127911a, b.}

Family SCHIZOPHORHDAE

Schuchert

and LeVene,

1929 Genus

SCHIZOPHORIA

King, 1850

SCHIZOPHORIA SULCATA

Sanders,

new

species Plate 3,C, figures 8-22

Exterior.

—

Shell transverse, a^littlewider thanlong, widest at

mid-

length; margins

rounded

;hinge line straight;cardinalmargins obtuse to

rounded

; lateral profile biconvex, with dorsal valvehaving greater convexity; anterior

commissure

rectimarginate; front

margin

slightly emarginate^; sulcus faint

on

both valves,

more

prominent

on

^dorsal

valve. Ventralinterarea gently apsacline,gentlycurved; beak faintly curved;

umbone

small, pointed; dorsal interarea orthocline, gently curved^; beak curved,

umbone

pointed. Surface multicostellate,

some

costellae hollow with holes leadingto exterior. Shell finely punctate.

Ventralinterior.

—

Delthyrial cavity deep; teeth stout, clublike, with posterior surface parallel to interarea

and

with small accessory sock- ets; crural fossettesoblique;dental plates locateddirectly

under

^teeth, but

forming

walls of delthyrial cavity

and

edge of delthyrium, con- tinued

forward

as ridges

bounding

muscle field; muscle fieldbilobate, divided

by narrow

ridge

whose

basewidensanteriorly to

form

raised, inverted

V-shaped prominence

^; adductors small, borne

on median

ridge; diductor scars elongate, divergent, each pair separated

by

a faint

low

ridge.

A

large trunk of the pallialsinuses originates atthe

forward

edgeof the diductor impression.

Dorsal interior.

—

Notothyrial cavity wide, deep,

bounded

by di- vergent, slightly curved brachiophore supporting plates,

which

are continued anterolaterally as faint ridges

bounding

muscle field; bra- chiophores stout, slightly recurved over dental sockets, not separable

from

supporting plates; fulcralplates curved, attached to inner over-

hanging

edge of palintrope; very faint denticlealong freeinner edge

44 SMITHSONIAN MISCELLANEOUS COLLECTIONS

VOL. II9 of palintrope, just lateral of sockets. Cardinal process prominent;

shaft a

narrow

septumlike ridge;

myophore

bilobate, with muscle

markings on

posterolateral sides; accessory cardinal processes pres- ent

on

floor of notothyrial cavity

between

shaft

and

brachiophore supporting plates.

Muscle

area large, divided

by

faint,

low median

ridge. Pallial sinuses prominent, four originating near

median

line,

two on

each side of the

median

ridge

and two more

at anterior ex- tremitiesof ridges separating adductors.

Types.

—

^Holotype,

U.S.N.M. 127915a

;figuredparatypes,

U.S.N.M.

I279i5b-h; unfigured paratype,

U.S.N.M.

127915.

Distinguishingcharacters.

— The

biconvexlateral profileofthis spe- cies is very characteristic

and somewhat

unusual for Schisophoria.

The

species is further distinguished externally

by

the sulcus

on

each valve, especially

by

^the

prominent

sulcus

on

the dorsal valve,a ^feature thatinspiredits

name.

This speciesresembles ^S. scdaliensis Weller, 1914, but that species lacks a sulcus

on

the dorsal valve. S. chouteauensis Weller, 1914, is also biconvex, but seems to have a deeper ventral valve

and

lacks the dorsal sulcus. Unfortunately the interior details of Weller's species are not well

known,

so other possible differences that

may

exist be-

tween

S. sulcata

and

the

two

species externally resembling it cannot be determined.

Remarks. — An

interesting

example

of repairof a shell break

made

during the lifetime of the animal is

shown

near the anterior

margin

of thespecimen figured

on

plate 3C, figure 17

(U.S.N.M.

I279i5e).

Suborder Strophomenoidea

Maillieux 1932

Family LEPTAENIDAE

Cooper, 1956

Genus

LEPTAENA

^{Dalman, 1828}

Leptaena

as here described follows the long usage expressed in Weller (1914)

and

elsewhere.

The

writer has

made no

attempt to trace the original usage

and

genotype todetermine if hisusage corre- spondsexactly to the^original.

McCoy

(1844, pp. 116-117) proposed Leptagonia based

on Pro-

ducta analoga Phillips, 1836, but

McCoy's name

has not been used because P. analoga Phillips has hitherto been regarded asa Leptaena.

The

interior of Phillips's species is

unknown,

so far as the writer is

aware, but

when known

might provide a basis for generic distinction, Leptaenella Sarycheva

and

Sokolskaja, 1952, alsobased

on Producta

analoga Phillips, is a

synonym

of Leptagonia

McCoy.

Furthermore,

NO, 3 MISSISSIPPIAN

FAUNA, SONORA — ^EASTON

^{ET AL.}

₄₅

the

name

Leptaenella is preoccupied

by

Fredericks (1917), ^for a

genus

based

on

Leptaena rhomhoidalisventricosa Hall, 1857a,Leptae- nella Sarycheva

and

Sokolskaja is thus a

homonym

as well as a

synonym and must

be discarded.

LEPTAENA COOPERI

Sanders,

new

species Plate 4,A, figures 1-5

Most

Mississippian leptaenas are referred toL. analoga (Phillips), 1836,a

Lower

Carboniferous species

from

England, butthe internal

morphology

of Phillips's species is still undescribed.

Rather

thanas- sign the present specimens to a widely used species

whose

interior is

poorly

known and where

interiors are unavailable forcomparison,the author erects a

new

species for these

Mexican

shells, based

on

their internal morphology. This

new

species appears to differ externally (andthe

few

interior details that can be seen

from

the illustrations)

from

the shells Weller (1914) assigned ^{to L.} analoga (Phillips)

and

also

from

L.

convexa

Weller.

Exterior.

—

Shell transverse, twice as

wide

as long, widest at hinge

line, flattened, planoconvex, with posterior portion of ventral valve gentlyconvex, correspondingpart of dorsal valve flat, sharply genicu- late anteriorly, the point of geniculation on the dorsal valve being sharply angular in front

and becoming more

obtuse

toward

cardinal extremities. Cardinal extremities acute, pointed^; front

margin

semi-

elliptical, slightly emarginate; hinge straight; ventral interarea apsa- cline, narrow, gentlyconcave^;beakslightlycurved; delthyrium closed at

apex by

a broad pseudodeltidium. Dorsal interareaanacline, nearly obsolete; beak only faintly pointed. Surface of both valves multi- costellate, with

much

^finer pattern of concentric lirae superposed

on

costellae; both of these modified

by

larger, irregular,

rounded

con- centric corrugations.

Ventral interior.

—

Notothyrial cavity broad, deep, semicircular,

forming

great

sunken

pitlike area for muscle attachment,

bounded

posterolaterally

by

thickened valve

margin

supporting teeth, anteri- orly

by

a curved elevated ridge,

apex

with triangular flattened area;

teeth blunt, elongate, clublike, crenulated, with long axis directed laterally, with

growth

track

forming

crenulatedarea

from

beak along outeredgeofdelthyriimi,

bounded

posteriorly

by

small accessory sock- ets

which merge

laterally intoa smallgroove alonginner edge of car- dinal area

and

apparently extending to cardinal extremity.

Muscle

areas occupying pitlike notothyrial cavity, with posterior portion smooth, undivided; separated for

most

of extent

by

^{a wide,}

rounded

46 SMITHSONIAN MISCELLANEOUS COLLECTIONS

VOL. II9