30 lophocercidjE. 



discovered it, believed the organs of respiration to con- 

 sist in the cilia, which fringe the fore-part of the body ; 

 but M. Blainville thinks the gill, unobserved, must have 

 been situated on the right-side, as in the genus Gastero- 

 pteron. 



Fain. LOPHOCERCID.E. 



Head with two ear-like tentacles ; eyes sessile on the 

 sides of the head. Gill regular, pectinate. Organs of 

 generation close together in one tubercle ; male organ on 

 the right side of the nape near the tentacle. 



Shell thin, involute, covered with an epidermis. 



Two fossil forms have been discovered by Dr. Philippi 

 in the Tertiary formation near Palermo, which he observes 

 cannot be referred to any existing genus, but which pos- 

 sibly belonged to animals closely allied to those of this 

 family. These extinct shells have received the names of 

 Aplysia? grandis, Phil, and A.? deperdita, Phil. 



Genus LOPHOCERCUS, Krohn. 



Body covered with papillse, and produced behind into a 

 long, pointed tail. Foot with the natatory appendages un- 

 divided, reflexed and partly covering the shell in front, 

 and united posteriorly. 



Shell involute, thin, ovate, covered with an epidermis ; 

 the outer lip separated from the last whorl, its hinder 

 angle inflexed, produced and rounded. 



Syn. ? Icarus, Forbes. 



Ex. L. Sieboldii, Krohn, pi. 59, fig. 1. Shell, L. 

 Sieboldii, fig. 1, a. 



In this curious genus (he head is truncate, and is 



