122 viTBimxjR. 



of the shell, and a reflexed appendage, which covers the 

 under side of the spire. Foot ahhreviate posteriorly. 



Shell internal, scutiform, oval, sub-spiral, flat, dilated 

 anteriorly. 



Ex. P. Valenciennii, Webb and Van Beneden, pi. 72, 

 fig. 4. Shell, P. Valenciennii, fig. 4, a. 



The Parmacellce, as properly restricted, inhabit Northern 

 Africa, with the exception of P. Valenciennii, which is 

 found in Portugal. They are herbivorous, feeding on the 

 young shoots of the Cochlearia acaulis. The shell is 

 furnished with a small hooked process, and there is a cor- 

 responding protuberance of skin on the back of the animal, 

 which fits between the hook and the margin of the shell, 

 and serves to retain it in its place ; an appendage of the 

 skin forms a fold, moreover, and is applied against the under 

 side of the callous rudimentary spire. M. Hang has 

 observed the species inhabiting Bourbon and Madagascar 

 (P. Rangiana) on the rocks at the margins of fresh-water 

 streams. 



Species of Parmacella. 



Alexandrina, Ehrenb. Valenciennii, Webb and 



Olivieri, Guv. Van Beneden. 



Rangiana, Fcrus. 



Genus CRYPTELLA, Webb and Berthelot. 



Mantle shield-like, ovoid, covering half the body, an- 

 teriorly free and linguiform, posteriorly saccate and covering 

 the shell, and received into a groove or pit on the hind part 

 of the body; orifice of respiratory sac at the right posterior 

 margin. Foot tapering, triangular, keeled above, pointed at 

 the end. 



