ORDER INFEROBRANCHIATA. 41 
other, to form an envelope for the gills, which are thus 
enclosed, as in a cylindrical case. 
They are small mollusca from the Indian Ocean. In the 
species known, (Placobranchus Hasselti, Cuv.) the branchial 
striz are green, and the body a brown grey, sprinkled with 
little ocelli. Van Hasselt; Bullet. Univ. Oct. 1824, p. 340. 
Messrs. Quoy and Gaymard found it at the Friendly Islands. 
THIRD ORDER OF GASTEROPODA. 
INFEROBRANCHIATA. 
THE Inferobranchiata have nearly the same form and organi- 
zation observed in doris and tritonia, but their gills, instead 
of being placed upon the back, resemble two long series of 
leaves, situated on the two sides of the body, under the pro- 
jecting margin of the mantle. 
PHYLLIDIA, Cuv. 
The mantle naked, usually coriaceous, and without any 
shell; the mouth a small proboscis, each side of which is fur- 
nished with a tentaculum ; two others project above from two 
small cavities in the mantle. The anus is on the hind part 
of the mantle, and the genital orifices forward, under the night 
side; the heart near the middle of the back; the stomach 
simple and membranous, and the intestine short. 
Several species inhabit the Indian Ocean. (Phyllidia tri- 
lineata, Seb., &c.) 
