MOLLUSCA. BRANCHIFERA. 
281 
BRANCHIFERA. 
I. Tribe. — NudibrancMa. 
a. Branchise 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. ^ 
Eolida. 
cc. 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. 
m. Branchiae single, when at rest concealed under a lid. Tectibran- 
CHiA. Marine, 
b. Head with tentacula. 
Aplysia. 
Pleurobranchus. 
hh. Head destitute of tentacula. 
Bulba. 
II. Tribe. — Pectinibranchia, 
a. Heart entire, and detached from the rectum. Cryptobranghia. 
««. Heart with two auricles, and traversed by the rectum. Scuti* 
branchia. 
