ROTELLA. 



Lam. Hist. Nat. des Aiiim. sans vert. vii. p. 6. 



TESTA subdiscoiclea, orbicularis, nitida; spira 

 brevissima, depresso-conoidea; facie inferiore 

 convexa, callosa; apertura oblique subtrigona, 

 labio externo acuto, basi subprominulo. Oper- 

 culum corneum, spirale, orbiculare. 



A PRETTY Geniis^ consisting of a few species^ separated 

 by Lamarck from the Linnean Trochus; its type is a very 

 common but elegant little shelly the T7\ vestiarius, While^ 

 on account of the very circumscribed character of the 

 genus we approve of the separation thus suggested by 

 Lamarck^ we are at a loss to discover a reason for his alter- 

 ing the specific name of the first species from vestiarim to 

 lineolata; wherefore we choose rather to retain the former 

 specific name and call it Rotella vestiaria: nothing can be 

 more variable in its colouring on both sides than this little 

 shell, for which reason we cannot approve of the term 

 infimd facie alba,' used in the specific character by 

 Lamarck. 



Shell rather discoid, orbicular, generally shining; 

 spire very short, of a depressed conical shape, the inferior 

 disk more or less convex, with a central, generally much 

 expanded callosity covering that part which in other dis- 

 coid shells forms the umbilicus. The aperture is gene- 

 rally obliquely triangular, sometimes almost square, with 

 rounded angles and the lower part of the outer lip is 

 rather prominent, so as to form between it and the umbi- 

 lical callosity an indistinct notch. It lias an orbicular, 

 spiral, horny operculum, very much like that of the Lin- 

 nean Trochus Niloticus and TurbQ Pica, 



