A, EK. Verrill—Mollusca of the New England Coast. 429 
the middle, tapering toward the posterior end and broadly rounded 
in front, so that the outline is somewhat conical, but truncated pos- 
teriorly. At the tip there is a small, but rather deep pit. The outer 
lip is thickened, somewhat constricted below the middle and then 
slightly expanded and broadly rounded anteriorly ; posteriorly it 
bends inward and projects slightly beyond the tip of the shell, and 
forms a distinct, rounded, posterior sinus. The columella-margin is 
thickened, without a fold, and moderately excurved. The umbilicus 
is narrow but deep. The aperture, in front of the middle, is moder- 
ately broad and ovate, but farther back it is much narrowed and en- 
croached upon by the body-whorl. The surface is smooth and pol- 
ished, without any sculpture except a few faint spiral lines close to 
the posterior end and others which are wavy and even less distinct 
at the anterior end. Color of the type-specimen, pure white, with a 
very thin yellowish white epidermis on some parts. 
Length, 6™™; greatest breadth, 4°"; length of aperture equal to 
that of the shell; its greatest breadth, 1:8™™. 
Station 2265, off Cape Hatteras, in 70 fathoms. (No. 44,657.) 
This species is readily distinguished from all others of our coast by 
its thickness and solidity, by its distinct umbilicus, and by the evi- 
dent pit at the posterior end. In form it somewhat resembles 
Diaphana conulus, but it is less narrowed posteriorly, besides being 
a much larger and stouter shell. 
Pleurobranchus Americanus Verrill, sp. nov. 
PLATE XLIV, FIGURE 13. 
In alcohol the body is oblong, higher than wide, with the mantle 
extending over the greater part of the shell. The foot is large, thick, 
with short, rounded, grooved auricles in front, its lateral surfaces, 
like those of the mantle, covered with small projecting spicules. Head 
bluntly: rounded, with two broad, leaf-like oral tentacles and two 
smaller and narrower posterior tentacles, which are flattened and 
folded ; on the left side there is a conspicuous dark blue eye behind 
the base of the dorsal tentacle, but on the right side the eye is con- 
cealed or wanting, in our specimen. The gill occupies the groove 
below the mantle on the right side, and is nearly one-third the 
length of the shell; just in front of the gill there is a low rounded 
prominence, with a central orifice. The shell is thin, translucent, 
pale yellowish white, oblong, with the sides nearly parallel and the 
anterior end bluntly rounded, The spire is a little prominent, ter- 
