MOLLUSC A.. 483 



The gut is short. The salivary glands are situate at the 

 folds of the stomach, and by two canals empty their con- 

 tents into the mouth. The liver is placed on the stomach, 

 and empties itself into the lower part of the crop. 



The heart is nearly in the middle of the back. Its auricle 

 is on the right side, at the base of the branchiae ; and the 

 ventricle sends out at the opposite side three arteries. 



M. CUVIER has figured and described the P. Peronii 

 with its anatomical details. Two species likewise appear to 

 be known as natives of the British seas. 

 B. Head destitute of tentacula. 



50. BULL A. Body of the ammal protected by a convolut- 

 ed shell. 



The body is, oblong, becoming a little narrower in front. 

 Below, the foot is broad, thin, and waved on the margin, 

 expanded on each side behind, and capable of being turn- 

 ed upwards. At the posterior part of the foot, but se- 

 parated from it by a groove, there is a broad, membra- 

 naceous appendage, a part of which is folded upwards, 

 and a part spread over bodies, like the foot. It assists 

 in closing the mouth of the shell, and in its position 

 and use is analogous to the operculum, in the follow- 

 ing order. Above the foot, in front, also, but separated 

 from it by a groove, there is a fat, fleshy expansion, which 

 CUVIER terms the Tentacular Disc, considering it as 

 formed by the union of the inferior and superior tentacula. 

 In the centre of the disc, in the Bulla hydatis *, MONTAGU 

 observed two eyes. Between this portion of the back and 

 the posterior extremity, is the dorsal plate or shell, forming 

 the genus Bulla of conchologists. In some species, this shell 

 is covered by the integuments, while in others it is ex- 

 posed. But in all, the part containing it is partially con- 



* Linn. Trans, vol. ix. tab. 6, f. 4. 

 H H % 





