174 MOLLUSCA. 



contains the branchiae. 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 Rariteitkamer, 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 branchiae are placed. The cloak 

 is strengthened in the middle, above the branchiae, 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 ofohese 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. 



