MOLLUSCA. BRANCHIFERA. 281 



BRANCHIFERA. 



I. Tribe. — NudibrancMa. 



a. Branchiae when at rest not covered by a lid. Nudibranchia. 

 b. Branchiae issuing from the cloak dorsally. 

 c. Body destitute of a shell. Marine. 



d. Anus situate near the posterior extremity of the back, 

 and surrounded with a fringe of plumose branchiae- 

 Doris. 

 Polycera. 

 dd. Anus on the right side unconnected with the branchiae, 

 . which are disposed along the back and sides, and un- 



connected with membranaceous expansions. Jaws 

 corneous. 



e. Tentacula two in number. 

 Tergipes. 

 Tritonia. 

 ee. Tentacula four in number. 

 Montagua. 

 EoUda. 

 ec. Body covered by a spiral shell. Lacustrine. 

 Valvata. 

 bb. Branchiae issuing latterly from between the cloak and the foot. 

 Body protected dorsally by a shell. Cyclobranchia. Marine. 

 Patella. 

 Chiton. 

 am. Branchiae single, when at rest concealed under a lid. Tectibran- 

 CHiA. Marine. 

 b. Head with tentacula. 

 Aplysia. 

 Pleurobranchus. 



bb. Head destitute of tentacula. 

 Bulba. 



II, Tribe. — Pectinibranchia. 



a. Heart entire, and detached from the rectum. Cbtptobbanchia. 

 aa. Heart with two auricles, and traversed by the rectum. Scon- 

 bramchia. 



