MOLLUSCA. PECTINIBRANCHIA. 361 



PECTINIBRANCHIA. 



SCUTIBRANCHIA. 



Heart with two 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. 



Crepidulid^e. 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. 



Capulid-E. Cavity and margin of the aperture entire. 

 Capulus. 

 (Carinaria.) 



Fissurellad^e. Cavity entire ; shell with a perfora- 

 tion or slit. 

 Fissurella. 

 Emarginula. 



Scissurella. 



