84 



Genus 23. ONISCIA, Sowerhi/. 



Animal; unkno2on. 



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

 depressed, base emarginated and a little recurved ; aperture 

 narrow, extending nearly to the apex ; columellar lip displayed 

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

 granular ^nmples ; outer lip irregularly denticulated, thickened, 

 sometimes a little contracted in the middle. 



This is one of the few genera established by modern authors which 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 tliat the scruples formerly enter- 

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

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

 by liis unqualified acceptation of it. Even Linnseus referred the typical 

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

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

 as being a "very singular" shell t; Mr. kSowerby first separated it under 

 the above title and it is now universally adopted. 



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

 sculptui'ed, and distinguished cliieily by the profusely granulated character 

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

 ably deep scarled-red colour. 



Species. 



1. cancellata, Soic. 3. oniscus, So%o. 5. tuberculosa, Sow. 



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



Figures. 

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

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

 latticed sculpture. 



* ]\I. Deshayes lias somewhat incautiously affinned, that the shell selected for the type of 

 this genus is not the Strom bus otusciis of Linnseus, but 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 Linnreus characteiized the aperture of his species 

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

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

 dicate otherwise. 



f " Petite coquiUe assez commune, mais tres singuliere ; car, quoique sou ouverture soit 

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



