MOLLUSCA. BRANCHIFERA. £81 



BRANCHIFERA. 



I. Tribe. — Nudibrancliia. 



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. 

 JMontagua. 

 Eolida. 

 ce. Body covered by a spiral shell. Lacustrine. 

 Valvata. 



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

 Body protected dorsallv by a shell. Cyclobranchia. Marine. 

 Patella. 

 Chiton. 



aa. 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. Cryptobraxchia. 



ma. Heart with two auricles, and traversed by the rectum. Scoti- 

 branchia. 



