106 



PATELLA. 



A. Furnished with an internal lip or chamber. 



(Plate XXI. Fig. 3.) (Fig. 4.) 



B. Margin angular, or irregularly toothed. 



(Fig. 5.) 



C. With a pointed, recurved apex. (Fig. 6.) 



D. Very entire, not pointed at the apex. 



(Fig. 7.) 



E. Having the apex perforated. (Fig. 8.) 



Shell univalve, conical, mostly without spire. 



The division C, consisting of shells with a re- 

 curved apex, forms a natural link between this 

 genus and the last described. The curvature of 

 the apex approaches more or less to a regular 

 spire, and in some species is precisely of the same 

 description as that of a Haliotis ; but, then, the 

 shell is not flat and ear-shaped, and therefore can- 

 not belong to Haliotis, or to any existing genus 

 but Patella, for there are none equally patulous 

 with these two. The gradations in the scale of 

 nature are in general so regular and yet so small, 

 that it becomes no easy task to trace the sepa- 



