MOLLUSCA. 477 



the anus. The salivary glands are small, and placed near 

 the mouth. The liver is large in proportion. 



The heart is placed in the middle of the back. The 

 auricle is simple, placed on the side next the tail, and sup- 

 plied by the two systemic veins which collect the aerated 

 blood from the branchiae on each side. There is a simple 

 aorta arising from the opposite side of the heart. 



The organs of generation appear to be similar to those 

 of the preceding class ; but they have not as yet been mi- 

 nutely examined. The existence of eyes is not satisfacto- 

 rily determined. 



The animals of this genus appear to be inhabitants of 

 the tropical seas. CUVIER has given descriptions and 

 figures of three species, which differ remarkably from one 

 another in the protuberances of the cloak. 



45. DIPHYLLIDIA. Anus placed on the right side. 

 This genus was formed by M. CUVIER in his Regnc 



Animal,, vol. hi. p. 395, from an imperfectly investigated 

 animal, in the cabinet of M. BRUGMANS at Leyden. The 

 cloak is pointed behind, with a feeler and small tubercle on 

 each side. 



2d Tribe. 



Branchiae simple, and concealed when at rest under a lid. 

 Tectibranchia of CUVIER. 



A. Head furnished with tentacula. 



1. Tentacula four in number. 



a. Branchise lateral. 



46. APLYSIA. Branchiae with a corneous lid. 



The body of the Aplysia is ovate, acuminated behind, 

 and produced before to form a neck. The foot is narrower 

 than the body. In the middle of the back is a corneous 

 plate inclosed in a bag in the skin, and on each side, and 

 behind, there is a fold by which this part may be con- 

 cealed. The head is slightly emarginatc, with a feeler on 



