MOLLUSC A OF PORTO RICO. 
367 
eyes about midway between them; mouth and lips small; dorsal furrow distinct in front, closed near 
dorsal slit, which is about one-third the length of the animal, situated behind the middle of the 
body, and not lateral; anus projecting as a large tube at the posterior end of slit; pleuropodia scarcely 
developed, of equal size, the right not projecting over the left. Surface pale lurid brown, covered with 
small mammillae and faint sharp pustules. Length, 50; diameter, 25; height, 18 mm. 
Shell elongated, solid, narrow at, and behind the apex, somewhat contorted, a concave depression 
running down the back, whitish and dull without, polished within. Length, 13; breadth, 5 mm. 
Hucares, Porto Rico, one specimen. 
Only the shell of D. sowerbyi has been described, and nothing is known of the soft parts of the 
species. The shell of this specimen agrees pretty well with Sowerby’s figures. 
Genus NOTARCHUS Cuvier, 1817. 
Ovate or fusiform, swollen in the middle. Pleuropodia united behind over a large gill cavity ; 
dorsal slit subcentral, short. Foot narrower than the body, acute behind. Shell minute or wanting. 
Type N. indicus Schweigger. 
Notarchus pleii Rang. 
Aplysia pleii Rang, Hist. Nat. Aplys., p. 70, pi. xxi, 1828. 
Body long ovate, very soft and flabby. Branchial cavity large, a little in front of the middle of 
the body; foot long, projecting behind, moderately wide. Surface more or less covered with filaments 
and variously lolled, ragged processes. 
Length of animal, 10 to 12 cm.; of branchial cavity, 35 mm. 
Boqueron Bay, Porto Rico, many specimens. 
Specimens in alcohol are most disagreeable, shapeless, flabby objects, of a dirty, bottle green. 
There is quite a little variation in the development of the filaments and processes on the body, some 
specimens being nearly covered with them and in others they are almost wanting. 
(Notaspidea.) 
Tectibranchs having the dorsal surface protected by a large shield. 
Family PLEU ROBRANCHIDiE. 
Gill plume arising about the middle of the right side and extending backward; dorsal shield 
fleshy; animal shell-less or having a small Haliotiform shell. 
Genus PLETJROBRANCHUS Cuvier, 1804. 
Body oval; mantle about the size of the foot, free and projecting at the edges all around; 
rhinophores contiguous, inserted below the mantle. Gill bipinnate. Shell auriculate. 
Type, P. peronii Cuvier. 
Pleurobranchus lacteus, n. sp. Plate 56, fig. 6. 
Body elliptical; mantle soft, inflated, faintly pustulous and wrinkled, semitransparent; foot 
smaller than the mantle, emarginate in front, having a wrinkled undulate border; rhinophores elon- 
gated, compressed, drooping and suddenly curved upward near the ends, extending in front of the 
veil and mouth; veil truncated in front, with a small projecting lobe at each corner; mouth round, 
with thick lips, extending as far forward as the veil; male and female orifices at the summit of a double 
mammilla situated just at the front of the gill plume; gill plume attached about midway back on the 
body, attached the front three-fifths of its length, and having about 20 pairs of plumelets; anus just 
above the. hinder point of attachment of the gill. Length, 22; breadth, 15 mm. 
Shell oblong, depressed, thin but solid, having about 2 whorls; spire full, mammillary; suture well 
marked and ending in an emargination behind ; growth lines developed into well-marked irregular ridges; 
surface covered with a thin, iridescent, whitish, or straw-colored epidermis. Length of shell, 5.5; 
breadth, 3 mm. 
Animal and shell milky white. 
Ensenada Honda, Culebra, five specimens. 
This species does not at all agree with any of the three forms described by Morch from the West 
Indies, and is probably new. 
