Family II. APLYSI'IDJE^Aplysida) D'Orbigny. 



BODY slug-like, semioval when at rest, but capable of con- 

 siderable extension, of a fleshy substance : mantle enveloping 

 the upper portion of the body, and covering the greater part 

 of the shell in those genera which have one: head snout- 

 shaped, prominent : mouth vertical, armed with large and 

 strong jaws: odontophore having in the middle a single row 

 of rhachidal teeth and on each side a row of numerous uncinate 

 or hook-like teeth : tentacles apparently 4, separate ; the front 

 or false pair resemble lips, and the hinder or true pair are 

 semitubular and not unlike the ears of a quadruped : eyes 

 small, sessile, in front of the hinder or true tentacles : foot 

 large, attached to the body throughout its whole length ; it 

 expands on each side, so as to form two lobes, which interfold 

 over the back and are in many genera used for swimming : 

 gills placed in a particular cavity or receptacle towards the 

 posterior part of the back, and protected by the mantle: 

 gizzard composed of several cartilaginous plates : vent placed 

 behind the branchial cavity. Each individual is of both sexes; 

 the organs of generation are separated and situate at the op- 

 posite extremities of the body. 



SHELL present in some genera only, usually internal and for 

 the most part concealed by the mantle ; it is shield-shaped, 

 thin, and slightly convolute at the smaller end, which is thick- 

 ened and furnished inside with a small tubercle or projection : 

 spire extremely short and terminal, coated over and concealed 

 in the adult, but heterostrophe in the fry : mouth extending 

 the whole length of the shell. 



The type of the present family is the famous sea-hare, 

 about which I will say something in its proper place. 

 Several genera have been described ; we have Aplysia 

 only. Although these animals resemble great slugs in 

 their general aspect, they have properly but a single 

 pair of tentacles, which are placed behind the eyes and 

 are not unlike the ears of a hare ; the two processes in 

 front, usually considered tentacles, are expansions of the 



VOL. v. B 



