MACROCHIRMA, 449 



Genus FISSURELLID.5CA, D'Oibigny. 



Mantle greatly developed, thickened at the edges, and 

 nearly covering the shell ; foot very large and elongated. 



Shell oval, depressed, surface nearly smooth ; perfora- 

 tion oval, large, central, with an internal, thickened rim 

 round the margin ; aperture very wide, with a thickened 

 callus round the inner margin, margin smooth. 



Ex. F. hiantula, Lamarck, pi. 51, fig. 4. Shell, F. 

 hiantula, fig. 4, a. 



In this genus the animal is of large size compared with 

 the shell, and the mantle is thick and almost coriaceous ; 

 there appear to be but few species, inhabitants of the 

 Cape, Tasmania, and South America. 



Species of FIssurellidiBa. 



sequalis, Sow. hiantula, Lam. 



Chemnitzii, Sow. nigrita, Sow. 



Genus MACROCHISMA, Swainson. 



Shell scutiform, elongated, surface radiately striated, 

 anterior extremity elevated, sub-emarginate, grooved 

 above; perforation large, ovate or lanceolate, elongate or 

 oblong, situated near the front edge. 



Ex. M. maxima, A. Adams, pi. 51, fig. 5. 



In this genus the animal, according to the observations 

 of Mr. Cuming, is of large size, larviform and greatly 

 elongated, with the shell situated towards the hinder ex- 

 tremity. The anal aperture or faecal perforation of the 



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