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ORDER II GASTEROPODA. 
Some are naked, others have a dorsal shell, not enveloping : again, others have a shell more or less 
hidden in their mantle. 
THIS Order is divided into two Sections Hydrobranchiae and Pneumobranchiae. 
SECTION I HYDROBRANCHLE. 
Contains Six Families, viz. Tritoniana, Phyllidiana, Semi Phyllidiana, Calyptraciana, 
Bullaeana, and Aplysiana. 
TRITONIANA. .G Genera. 
Without shells, either external or internal. 
Glaucus. — No shell. 
Eolis. — Ditto. 
Tritonia. — Ditto. 
ScYLL/EA. Ditto. 
Tethys. — Ditto. 
Doris. — Ditto. 
PHYLLIDIANA. _4 Genera. 
Some are without shells, either internal or external: others are wholly or partly covered by a shell, 
sometimes composed of one single piece, sometimes of a range of moveable and distinct pieces. 
Phyllidia. — Has no shell. 
Ciiitonellus. — Body elongated, rather narrow, like a caterpillar, the middle of the back 
furnished with a multivalve shell; valves alternate, mostly longitudinal; they are 
nearly connected by their extremities. 
Plate XIII. Fig-. 11. C. striatus. [Mrs. Mawe’s Cabinet.] 
Chiton. — Body oval-oblong, convex, rounded at the extremities; bordered allround by 
a coriaceous skin; partly covered by a longitudinal series of testaceous, imbri- 
cated, transverse, moveable pieces, set in the borders of the mantle. 
Plate XIII. Fig. 12. C. Magellanicus. (Idem.— Gmel.) 
Patella. — Shell univalve, not spiral, covering the animal, shield-like, or retuse-conical; 
concave and simple below, without any fissure on the margin; the summit entire, 
and inclined anteriorly. 
Plate XIII. Fig. 13. P. miniata. (P. sanguinolenta. — Gmel.) 
(a) Inside of ditto 
SEMI-PHYLLIDIANA 2 Genera. 
Pleurobranchus. — Shell internal, dorsal, thin, flattened, often oblique-oval. 
Plate XIII. Fig. 14, 14 («). P. plumula. (Bulla pluinula.— Montagu.) 
E 
