46 CLASS III. GASTEROPODA. ORDER IV. PLEUROBRANCHIATA. 
Examples. 
Pl. CLIL. Fig. 1. 
VERMETUS LuMBRICALIS, Lamarck, Anim. sans vert., vol. vi. p.225. De 
Blainville, Manuel de Malacologie, pl. 34. f. 1. 
Le Vermet, Adanson. 
Serpula vermetus, Sowerby. 
Pl. CLII. Fig. 2. 
VeERMETUS EBURNEUS*, Nobis, Proceedings Zool. Soc., 1842. 
Order IV. GASTEROPODA PLEUROBRANCHIATA. 
Branchie latere dextro semper imposite, seu sub margine pallii, seu in 
cavitate speciali. 
This order is intended for the reception of certain mollusks which have 
their branchiz situated on the right side only of the body, whether placed 
under the edge of the mantle, as in the order Cyclobranchiata, or in a par- 
ticular cavity, as in most of the Cervicobranchiata. A very natural group 
of animals is thus brought together, which are as closely allied by other 
and perhaps more important affinities. The Pleurobranchiata are not all 
conchiferous, and the greater part of those that are, have merely a thin, 
horny shell concealed within the mantle, either on the back, or over the 
branchial cavity. 
They are divided into three families, as follows : 
BuLuacga. APLYSIANA. 
SEMIPHYLLIDIANA. 
* This beautiful species was brought by Mr. Cuming from South America. 
