SCISSURELLA. 



jyOrhigny, 



TESTA univalvis, libera, urnbilicata, spira de- 

 pressa, apertura subrotunda, labiis disjunctis, 

 canali nullo,peristomate acuto; foramine oblongo 

 prope marginem dextram incrementum an- 

 fractuum sequente et carinam in dorso testae 

 efFormante. 



I HAVE already, in the Zoological Journal, vol. I. p. 255, 

 explained my reasons for regarding this genus as distinct 

 from Pleurotomaria of De France. 



First discovered by M. Alcide Dessalines D'Orbigny, 

 in prosecuting his researches among the marine and fossil 

 sands of various countries, in order to study the micros- 

 copic Cephalopoda which are found in them. I apprehend 

 that all the specimens which may have come under the 

 observation of M. D'Orbigny, must have been more or 

 less imperfect or very young shells, for he describes the 

 upper part of the right lip as " notched, with a deep slit," 

 whereas, in several which I have selected from the fossil 

 sand of Grignon, the margin of the right lip is entire, 

 and an oblong foramen reaches very nearly to the edge, 

 but not quite; at the same time in a recent specimen, 

 which is much smaller, the margin is notched with a deep 

 slit as D'Orbigny describes it. Whether, however, the 

 real character of the genus consist in a deep notch in the 

 upper edge of the right lip, or an oblong foramen reach 

 ing nearly to the edge, we think it properly arranged near 

 to Fissurella or Haliotis, because its affinity appears to be 

 nearer to those genera than to the Trochida?. 



Shell univalve, free, with an umbilicus and a depressed 

 spire; aperture nearly round; the lips separated from 



