CONTENTS OF VOL. II. XXX1X 
Page. 
B. Shells depressed. Planorbis. Segmentina. . 462 
Tribe II. Shell conical. Ancylus. ; : 463 
Subdivision II. Body destitute of the protection of a 
shell. Peronia. : : . ib. 
Class [1.— Branchifera. 
Order I. Branchiz external. 
Tribe I. Branchiz exposed. 
A. Branchiez issuing from the cloak dorsally. 
1. Body exposed, and destitute of a shell. 
a. Doris, Polycera. 5. Tergipes, Tritonia, Montagua. 
Eolida, Scyllaa, Glaucus, Thethys. : 466 
2. Body concealed in a spiral shell. Valvata. : 472 
B. Branchie issuing laterally from between the cloak 
and foot. 
1. Body with a shell. Cyclobranchia. Patella, Chi- 
ton, Chitonellus. . L : 475 
2. Body naked. Inferobranchia. Phyllidia, Diphyl- 
lidia. 476 
Tribe II. Branchiz simple, and concealed when at 
rest under a lid. Tectebranchia. 
A. Head furnished with tentacula. ‘i 
1. Tentacula four in number. a. Aplysia, Notarchus. 
b. Dolabella. : ATT 
2. Tentacula two in number. Pleurobranchus. - 480 
B. Head destitute of tentacula. Bulla, Doridium. 483 
Order II. Branchiz Internal. 
‘Subdivision I. 
Heart entire, and detached from the rectum. 
Tribe I. 
Shell external. 
