174 MOLLUSCA. 
contains the branchiz. The position and structure of the 
other organs are precisely similar to those of the Aplysia. 
This genus was instituted by Lamark, from characters de- 
rived exclusively from the dorsal plate or shell. Cuvier 
afterwards examined a species brought from the Mauritius 
by Peron, which he considers as the one figured by Rum- 
phius in his Amboinshe Rariteithamer, tab. x. No. 6, and 
which he has consecrated to his memory, naming it Dola- 
bella Rumphii. 
Genus PLEUROBRANCHUS.—Tentacula two in num- 
ber. Cloak and foot expanded, between which, on the 
middle of the right side, the branchiz are placed. The cloak 
is strengthened in the middle, above the branchia, by a thin 
expanded subspiral shell. The neck is short, and in some 
contracted, with the front emarginate, exhibiting the com- 
mencement of the inferior tentacula. The upper tentacula 
are tubular and cloven. The gills occur at the edge of the 
dorsal plate. In front of-these are the orifices of the organs 
of generation, and the anus is situate immediately behind 
the gills. The mouth is furnished with a short retractile 
proboscis. The tongue occupies both sides of the mouth, 
and is covered with spines. The gullet is enlarged into a 
kind of crop before it enters the stomach; this is folded, and 
is divided by contractions into three parts. ‘The first sto- 
mach has muscular walls of moderate thickness, with a single 
longitudinal band. The second has membranaceous walls, 
with longitudinal internal ridges, and the third has thin and 
simple walls. The gut is short. The salivary glands are 
situate at the folds of the stomach, and by two canals empty 
their contents into the mouth. ‘The liver is placed on the 
stomach, and empties itself into the lower part of the crop. 
