24 CLASS III. GASTEROPODA. ORDER III. CERVICOBRANCHIATA. 
Pl. CXL. Fig. 8. 
EMARGINULA FISSURATA, Sowerby, Genera of Shells, No. 34. f. 3. 
Patella fissurata, Chemnitz. 
Emarginula rubra, Lamarck. 
FISSURELLA, Bruguiere. 
Testa ovata vel oblonga, depresso-conica, clypeiformis, margine levi, 
raro crenato ; vertice antico, perforato ; foramine irregulari, plerum- 
que oblongo, striis seu radiis ad marginem decurrentibus. Im- 
pressio muscularis anticé latior, interrupta. 
The distinguishing character of the Fissurellze is that of having their 
shell perforated at the summit, for the purpose of conveying the water to 
the respiratory cavity. This perforation, which is generally of an oblong 
oval shape, was especially noticed by the early naturalists ; and although 
the Fissurellee or Key-hole Limpets were usually regarded as distinct from 
the Patelle or Common Limpets, they were not elevated by those authors 
to the rank of a genus. Bruguiére was the first to accomplish this de- 
sirable separation, and the propriety of it has been singularly confirmed 
by the later discovery of the important difference in the arrangement of 
the branchiz. The genus Fissurella has now become one of consider- 
able interest on account of the many beautiful new species that have been 
contributed by the exertions of Mr. Cuming ; most of their shells exhibit 
an elegant variety of painting, and are highly esteemed by collectors. 
The shell of Fissurella may be described as being ovate or oblong, and 
shaped like a shield or depressed cone ; the margin is smooth, very rarely 
crenated ; the vertex is anterior, and perforated, the orifice being generally 
irregular and oblong ; and the outer surface is ornamented with variously 
coioured striz or rays, running from the margin of the orifice down to 
the basal margin. The muscular impression is wider on the anterior 
side, and interrupted. 
