FISSURELLA. 



TESTA clypelformis, aut depresso-conica, ple- 

 rumque oblonga, subtus cava; vertice antico, 

 pertuso: striis plerumque ex vertice ad inar- 

 ginem deeurrentibus, lineis incrementi decus- 

 satis. Impressio muscularis lateribus anticis 

 latior. 



The Fissurellae were formerly associated with E^nargimda, 

 Parmophorm and other modern genera, under the generic 

 name Patella; several of these agree very nearly in their 

 general form, but are distinguished by certain peculiai'i- 

 ties which characterize in some instances a considerable 

 number of species : those which are referable to the pre- 

 sent Genus, are remarkable for having the vertex perfo- 

 rated, which character will prevent their being confounded 

 with any other. This Genus was separated from Patella, 

 by Bruguiere, because he considered the perforation of 

 the vertex as an indication of remarkable diversity in the 

 structure of the animal, sufficient to warrant the separa- 

 tion; a fact which has been confirmed by Beudant and 

 others who have had the opportunity of examining it 

 alive. 



The general form of the Fissurellae is that of an 

 oblong and rather convex buckler, or of an oblong de- 

 pressed cone ; hollow beneath, and having the point of 

 the vertex directed to the front of the shell, and per- 

 forated : this perforation, which serves for the passage 

 of the water to the branchiae and of the excrements, is 

 occasionally nearly round; mostly of an oblong shape, 

 in some species contracted at the center, in others widen- 

 ed, and the shell is always thickened around the margin 

 on the inside, as if the edge were turned inwards. The 



