54 CLASS III. GASTEROPODA. ORDER IV. PLEUROBRANCHIATA. 
branchiz. ‘The Aplysiz are not all conchiferous, nor do they in any 
case exhibit more than an internal membranaceous shell, inserted in 
that part of the mantle which covers the branchial cavity. It may be 
described as being rather convex, somewhat compressed, very thin, and 
always horny ; the posterior side is a little acuminated, with the vertex 
somewhat beaked inward, and the anterior side is rounded. 
Examples. 
Pl. CLVI. Fig. 1 and 5. 
AptysiA Petersoni, Sowerby, Genera of Shells, No. 39. 
Pl. CLVI.: Fig. 2. 
AprysiA Brasitiana, Rang, Hist. Nat. des Aplysies, pl. 8. f. 1 to 3. 
Deshayes, new edit. of Lamarck, vol. vii. p. 691. 
Pl. CLVI. Fig. 3. 
Ap.ysia concava, Sowerby, Genera of Shells, No. 39. 
Pl. CLVI. Fig. 4. 
ApLysia quapRATA, Sowerby, Genera of Shells, No. 39. 
DOLABELLA, Cuvier. 
Testa interna, calcarea, interdum subcornea, dolabriformis, integumento 
corneo sepé induta ; posticé angustata, crassior, callosa, subspiralis, 
margine subreflexo ; anticé planulata, latior, margine integro. 
The Dolabellze were distinguished by Cuvier, in the first place, owing 
to an evident change in the structure of their shells; and, in the second 
place, owing to their being for the most part solid and calcareous ; they 
are nevertheless so closely allied to the Aplysie in their organization and 
