BCLLA. 329 



themselves are mostly not thoroughly differentiated into " species," 

 if by that term we understand isolated and unconnected races. 

 There are, however, geographically restricted forms which in their 

 average features constitute moderately tangible races; and ratherthan 

 lose sight of these average differences which are certainly correllated 

 with geographic range, we have herein recognized the conventional 

 <l species " based upon them. To some minds who hold the " species " 

 to be a sacred fetich, the course of the " lumper" would be more 

 acceptable ; and they may write all there is of the striata group of 

 Bulla, under that name. It is simply a question of what degree or 

 grade of racial deviation is worth formal recognition in nomencla- 

 ture ; and this must in the nature of things, remain a question of in- 

 dividual opinion. 



(Group of B. striata}. 



1'nder B. striata the genesis of the various races of this group is 

 discussed. 



B. AMYGDALA Dillwyn. PI. 38, figs. 49, 50, 62, 63, 64, 65 ; pi. 39, 



fig. 79. 



Shell oblong, somewhat cylindrical and narrower toward the 

 vertex, solid, heavy and strong, not very shining, clouded and mottled 

 indistinctly with purplish on a pale ground, more or less obviously 

 spotted or blotched ivith deep purple or blue-black, the spots shading 

 into the ground color on the left side, whitish-margined on the right 

 side of each. Surface showing under the lens no microscopic spiral 

 ttr'mtion (such as occurs in B. striata, occidentalis and solida), but 

 having some spaced spiral impressed lines toward the base, and occa- 

 sionally a few near the vertex, but these are more often absent. 

 Vertex not especially compressed having a deep and rather large 

 apical umbilicus, which is more or less lirate within. Outer lip thick, 

 heavily calloused where it rises from the vertex; its outer portion 

 straight, not convex; base broadly rounded. Columella arcuate, 

 with a very heavy reftexed crescentic callus, the outer edge of which is 

 well raised from the whorl throughout, leaving a chink behind it; 

 parretal callus strong and white ; interior lined with a white callus. 

 Alt. 40, diam. 23 mill. Some adults are smaller, alt. 26, diam. 15 

 mill., and others larger, alt. 46, diam. 27 mill. 



St. Thomas, Tortola, Curaeoa and Gulf of Paria (Robert Swift !) ; 

 West Indies generally. 



