84 

 Genus 23. ONISCIA, Sowerby. 



Animal ; unknown. 



Shell ; oblong, somewhat cylindrical, or conical, spire short and 

 depressed, base emarginated and a little recurved j aperture 

 narrow, extending nearly to the apex ; columellar lip displayed 

 over the body whorl, more or less profusely covered with small 

 gra?udar pimples ; outer lip irregularly denticulated, thickened, 

 sometimes a little contracted in the middle. 



This is one of the few genera established by modern authors winch it 

 is desirable to maintain ; though unacquainted with the soft parts, the shell 

 sufficiently indicates the presence of some concurrent peculiarities worthy 

 of distinction, and I am glad to observe that the scruples formerly enter- 

 tained by M. Deshayes to the adoption of tins genus, noticed by me in the 

 'Conchologia Systematica', have been removed in the 'Anim. sans vert/ 

 by Ins unqualified acceptation of it. Even Linnaeus referred the typical 

 species of this group to a different genus from that in winch he included 

 the Helmets * and Lamarck in placing it with the Cassidaria, describes it 

 as being a "very singular" shellf; Mr. Sower by first separated it under 

 the above title and it is now universally adopted. 



The Oniscia are very limited in number; they are most elaborately 

 sculptured, and distinguished chiefly by the profusely granulated character 

 of the columella, which in the species figured, 0. Bennisoni, is of a remark- 

 ably deep scarled-red colour. 



Species. 



1. cancellata, Sow. 3. oniscus, Soto. 5. tubercidosa, Sow. 



2. Dennisoni, Reeve, 4. Strombiformis, Reeve. 



Figures. 

 Oniscia Dennisoni. PL 7. Pig. 35. Shell, a, front view, showing the 

 aperture and granulated columella ; b, back view, showing the rich 

 latticed sculpture. 



* M. Deshayes has somewhat incautiously affirmed, that the shell selected for the type of 

 this genus is not the Strombus oniscus of Linnseus, hut one differing even generically from it. 

 "There are two species" says the learned editor of the 'Anim. sans vert.' one of which he re- 

 tains in Cassidaria, whilst he refers the other to Oniscia with a complimentary dedication to 

 Lamarck, " closely approximating, which may be easily distinguished by the denticulations of the 

 outer lip and a difference of colour, for whilst Linnaeus characterized the aperture of his species 

 as being white, Lamarck says it is red." These modifications cannot, I think, be accounted of 

 specific, much more of generic value ; and I see nothing in the figures of Gualter or Seba to in- 

 dicate otherwise. 



f " Petite coquille assez commune, mais tres singuliere ; car, quoique son ouverture soit 

 celle des Casques, sa queue n'est point brusqucment rctroussee comnie dans ce dernier genre ". 



