DIPTERA OF NORTH AMERICA, [PART IV

inthe

groups

in wliichthey prevail^; buttheir

importance

arises

from

their characterizing the great majority of the species^:

—

1. In the T. longipalpi, the auxiliary vein ends in the first longitudinalvein,being incurved

towards

it;

beyond

the

humeral

cross-vein there is

no

other cross-vein connecting the auxiliary vein

with

the costa or with the first longitudinal vein. In the T.hrevipalin the auxiliary vein,as a rule, ends in the costa,

and

isconnected

by

across-vein with the firstlongitudinal vein.

2.

The

structure of the cells in the vicinity of the

stigma

is totally differentin the

two

divisions.

The

firstlongitudinalvein inthe T. loyigijjalpi isusually incurved

towards

the

second

vein

and

attenuated in a peculiar

manner

before

ending

in it;

an

oblique cross-vein connects the firstvein, a short distance

back

of the tip, with the costa^; this cross-vein, together with the anterior

branch

of the second vein,

form

near the anterior

margin

a small, trapezoidal cell, very characteristic of the T.

longijMlpi (it is wanting, however, in

Dolichopeza and some

related species). In the T. hrevipaJpi the first longitudinal vein ends in the costa,

and

the cross-vein, at its tip or

some

distance beforeit, connects itwith the secondlongitudinal vein_; no structure likethe trapezoidal cell isapparent.

3.

The

structure ofthe discal cell

and

the direction of the veins surroundingit is different in the

two

divisions. In the T.

longipalpi, the vein separating the

two

last posteriorcells (the posterior intercalary vein of

Mr. Loew

;

compare Monogr. of N.

A. Diptera, I, p. xxiv, fig. 3, v) issues very near the inner

end

of the discal cell, usually

from

the angle,

between

this cell

and

the great cross-vein; this, in

most

cases, gives the cell a pentagonal shape, unless, as for instance in the

genus Pachyr-

rhina, the vein has

no

contact atall with the cell,

and

has the appearance of the direct prolongationof the fourth longitudinal vein; in such cases the discal cell is a parallelogram. In the T. hrevipalpi the posterior intercalary_ vein issues from the latter

end

of the discal cell,

and

its origin is quite distant

from

the greatcross-vein,

which

is usually nearthe inner

end

of the discal cell.

The Amalojnna show some approach

to the T.

longipalpiinthe position of the intercalaryvein

and

intheshape of the discal cell; still the origin of the intercalary vein inthe

Amalopina

is usuallyrather distant from the great cross-vein.

Amalopis

vernalis 0. S., is the only species which, in this

INTRODUCTION. 19 respect, is like the T. longipalpi; the intercalary vein of this species issues from the angle

between

the cross-vein

and

the discal cell, atthe inner

end

of the latter.

4. Inthe T. longipalpi a distinct fold generally runs across the

wing from

the inner

end

of the stigma, over the discal cell, to the penultimate posteriorcell; itis usually

marked by

apaler coloringof the

membrane

of the Aving

and by

a discoloration of tlie wing-veins; it is

more

or lessdistinctin the diiferentgenera.

In the T. brevipalpi this fold is not apparent,

and

a slight trace of it

may sometimes

be observed in the partial discoloration of the veins at the inner

ends

of the discal

and

of the penultimate posteriorcells.

5.

The

T. longipalpi usually

keep

the

wings

divaricate in repose, while the T. hrevipaljoi fold

them

over the

abdomen.

Pedicia,

which reminds

us of the longipalpi

by

the length of the lastjoint of the palpi, alsokeeps the

wings

divaricatein repose.

6.

The rostrum

of the T. longipalpi is usually

more

pi'olonged

and

its

upper

part projects in the shape of a point (?msi<.9),

clothed with hair; a very

marked

character,

seldom wanting among

the T. longipalpi,

and

notobserved

among

the T. brevi- palpi.

t.

The

antennae of the

normal

types of T. longipalp)i are 13- jointed; those ot the T. brevipalpi are

from

14 to 16-jointed;

exceptions are comparatively rare.

The

structure of the joints of the fiagellum,

common among

the T. longipalpi, is different

from

thatof themajority of the T. brevipalpi.

8.

The male

genitals ofthe T. longipalpi are of a

more com-

plicated structure

and more voluminous

than the simple forceps of the T. bi^evipalpi; still, in this respect, intermediate forms occur.

9.

The

size of the T. longipalpi is generally considerably larger; theirfeet

and

especiallythe tarsi, are longer.

The

Ptychopterina, as I

have

said above, are an

anomalous

group,

which

does not well fit in either of the

two

principal divisions of the Tipididse.

Their

palpi arelong; butthis length

depends on

the elongation of all the joints

and

not of the last joint in particular; this applies especiallyto the

genera

Proto-

plasa

0. S.

and Tanyderus

Philippi.

The

auxiliary vein in

Bittacomorpha and

Pfychoptera

ends

in the costa,

and

thereis

no

cross-vein connecting it with the first longitudinal vein; in

20.

DIPTERA

OF

NORTH AMERICA. [PART

IV.

Frotoplasa and Tanyderus,

^{thiscross-veinexists,}

and

itsposition is altogether as in the T. hrevipalpi.

The

rest of the venation of the Ptycliox)terina ^is peculiar

and

distinguished

by

the absence of the sixth longitudinal vein; still this venation is

more

like that of

some

T. hrevijMJpi, than of

any

T.

UmgipaJpi;

there is

hardly

any

vestige ofafold across thewing.

The

general appear- ance

and

the coloring of the

body and

of the

wings

are

much more

likethe T.hrevipalpi; the structureof the antennas

and

the

number

of their joints also

remind

us of them.

The

elongated epistoma,

however,

in

Bittacomorpha and

Ptyclioptera,

shows something

of the

nasus

peculiar to the T. lovgipalpi; it is not apparent in Protop)Jasa.

The

PfycJiopterina

keep

.the

wings

divaricate inrepose (I

do

not

know whether

thisappliesequally toProtoplaaa).

In the Cylindrotomina, the course of the auxiliary

and

first longitudinal veins strongly

remind

usofthe T. longipalpji; the T.

h7\^.vipalpiwith a single

submarginal

cell, as far as

known,

never

have

spurs at the tip ofthe tibia-,

whereas

the

Cylindrotomina

partake of both of these characters at the

same

time; the T.

brevipaljn with asingle

submarginal

cell

always have

only four posterior cells,

Cylindrotoma

distinctissima

and

G.

americana have

a single submarginal ^cell

and

five posterior cells.

At

the

same

time,the

number

oftheantennaljoints ofthe

Qylindrotomina

(16), the position of the posterior intercalary vein

and

the struc- ture of the palpi, are charactersbelonging to the T. hrevipalpi.

The

Cylindrotomina, except in the

above quoted

instance,

have

four posterior cells, a characterof

common

occurrence

among

the T. hrevipalpi, and, as fdr as I

know,

not observed yet

among

the T. longipaljn.

(Compare,

for

more

detail, the chapteron the Cylindrotomina.₎

Thus, if

we

adoptthe division into T. longipaljn

and

T. hrevi- palpi, itwill

be

necessary to form a third

group which

will be artificial

and

contain the intermediate

and anomalous

forms.'

1 Itwaswiththisintention thatIintroducedinthefirstvolumeofthe presentseries [Monographs, etc.,Vol. I, p. 11) thegroupPtijchopierina, co- ordinatewiththe T. loncjipalpiandhrevipalpi (followingMr. Loew'sprece- dence,IthencalledthemTipuliiiaandLimnohina).

With

theCylindrotomina

Iwashardly acquaintedatthat time, asIhadfound onthiscontinent only a singledouhtful specimen. It

may

notbe amisstonotice here,that the two last lines ofthe above quoted page contain a lajisus calami, which

INTRODUCTION.

²¹