OPISTHOBRANCHIATA FEOM THE ABEOLHOS ISLANDS. 539 
Pamily PLACOBRANCHID.E. 
The head is flattened, and passes over laterallj' into short leaf- or ear-shaped 
tentacles, which have their lateral margins rolled. The two closely set eyes 
show through the skin of the neck. The body is much flattened and its sides 
or mautle-folds expanded into wing-like flaps (these are not epipodial 
developments as in Tethys), which are usually held up over the body. Behind 
the neck is a noticeable swelling, the pericardial swelling containing the 
pericardial cavity and the kidney, and at the right side of this lies the anus. 
The dorsal surface of both body and lateral expansions generally bears a series 
of low longitudinal folds or lamella3. The foot is not sharply marked off 
from the body, its edge projects very slightly, and often its anterior end is 
bilabiate. 
There are no jaws ; the radula is short, uniseriate, and has large teeth. 
These, when worn, are shed into the inferior radula-sac. The stomach is 
short and sac-shaped. The hermaphrodite gland is not discrete, but in the 
form of isolated follicles. The penis is protrusible and armed with a curved 
spine. 
Genus Placobeanchus van Hasselt, Alg. Konst en Letter-Bode, 
1824, I. Deel, no. 3, p. 34. 
Type by monotypy, P. ocellatus v. Hass. 
The head is flattened, with a broad front, which bears on each side a short 
leaf-like or auriform tentacle whose side-margin is rolled. Two eyes, set 
close together, lie on the neck. The body is much depressed and bears two 
wing-like lateral expansions ; these are mantle-lobes belonging to the body 
and not epipodial appendages as in Tethys ; they are usually turned up oyer 
the body. Behind the neck is a fairly large pericardial swelling, on the 
right side of v/hich lies the anal aperture. The upper surface of the body 
and the mantle-lobes bear numerous, longitudinal, parallel, low folds. The 
double genital aperture lies behind the right tentacle. The foot is not 
distinctly marked off from the body, anteriorly it is divided by a transverse 
groove into two equi-sized lips. 
The bulbus pharyngeus is much as in Phyllobranohia. The radula is 
short and uniseriate, the teeth are large and persistent and passed on into 
an inferior sac. The penis is armed with curved spines. 
Species Placobeanchus expansa, sp. nov. (PI. 27. fig. 4 ; PI. 29. figs. 31-34.) 
Body. The body of this form is extremely flat and somewhat elongated. 
It passes out without a sharp line of demarcation into the enormously developed 
mantle-lobes which project, as leaf-like expansions, many times the width of 
the body and are continuous behind with the posterior end of the body. The 
whole animal presents the appearance of a flat leaf slightly thickened in the 
