MOLLUSC A. PECTINIBRANCHIA. 361 



PECTINIBRANCHIA. 



SCUTIBRANCHIA. 



Heart with tivo auricles traversed by the rectum; sexes incorporated ; 

 body covered with a patulous shell; the foot destitute of a lid. 



I. Shell ear-shaped, with a lateral and nearly concealed spire. 



Haliotis. 

 (Padola.) 

 (Stomatia.) 



II. Shell oblong or conical, simple or subrevolute. 



Crepidulidj^:. Cavity of the shell interrupted by a testaceous 

 plate. 



a. Marine. 



b. Plate of the cavity spirally decurrent. 

 Calyptraea. 

 Infundibulum. 



bb. Plate of the cavity horizontal. 

 Crepidula. 

 Pileolus. 



aa. Fluviatile. 



Navicella. 



CapulidjE. Cavity and margin of the aperture entire. 

 Capulus. 

 (Carinaria.) 



FissuRELLAD^. Cavity entire ; shell with a perfora- 

 tion or slit. 

 Fissurella. 

 Emarginula. 



Scissurella. 



