FISSURELLA. 445 



exhibit an affinity with the Trochidce and Hnliotida<, but 

 their eyes are not situated at the ends of separate peduncles, 

 and their shells are not nacreous or pearly within. The 

 nucleus is always spiral, although, in the adult, the shell 

 assumes a conic form ; in some genera there is a rudi- 

 mentary spire in the young state, which disappears in the 

 course of growth. The perforation or fissure of the shell, 

 though sometimes regarded as branchial, is undoubtedly 

 faecal in its office. 



Genus nssuRELLA, Bruguiere. 



Mantle-margin fringed with cirrhi ; anal siphon a short, 

 truncate, membranous canal, projecting from the perfora- 

 tion in the shell. 



Shell oval, conical, depressed, surface radiated or can- 

 cellated ; apex truncate and perforated in front of the 

 centre ; aperture wide, expanded, oblong, simple internally. 



8yn. Larva, Humph., not Veill. Caminata, Fahr. 

 Fissurellus, Montf. Serra, Less. 



Ex. F. maxima, Sowerhy, pi. 51, fig. 1. Shell, F. 

 picta, Gnielin, fig. 1, a. 



In the young shell the apex is entire and sub-spiral, and 

 the perforation is situated in the same position in which 

 it exists permanently. The species are found in nearly 

 all countries, but are most numerous along the coasts of 

 South America. 



Species of Fissurella. 



atrata, Reeve. catillus, Beeve. 



bella, Reeve. Cliilensis, Sow. 



biradiata, Fremb. clypeus, Son-. 



Bridgesii, Reeve. costata, Less. 



