82 University of 3Iicliigan 



istic of most of the species in the Dutch Leeward Islands), 

 and, as a result, the spiral bands are seldom continuous for 

 any distance. Forty per cent, of the shells may be classed as 

 flammulated. In this group are included the shells in which 

 the varices are broken by non-pigmented spiral zones, and also 

 those in which the continuous or broken varices are flammu- 

 lated by spirally arranged blotches of color. In 30 per cent, 

 of the shells, the broken, spiral bands and varices are about 

 equally prominent, so as to form grid markings. Twelve per 

 cent, may be classed as spirally banded, although only one 

 specimen (from B8) has truly continuous, spiral bands for 

 any distance. Usually, the spiral bands are lightest where the 

 growth lines are farthest apart; this produces a series of con- 

 tiguous, oblong blotches, each of which shades from light to 

 dark in the direction of growth. 



Peristomal callus and edge of columella : usually white, 

 bordered internally by a dark, chocolate band ; sometimes the 

 entire callus is colored practically as dark as the interior of 

 the aperture. 



Interior of the aperture : almost white to dark chocolate, 

 usually darker than the exterior of the shell, but varying in 

 intensity of color with it. Commonly the spiral bands and 

 varices are also darker and broader than on the exterior. 



In addition to the color variation, the shells vary consider- 

 ably in size and shape, and in solidity. The shells from Aruba 

 are the lightest and smallest, while those from Bonaire are the 

 largest and most solid. The comparatively small numbei*s of 

 specimens make the following dimensions studies less trust- 

 worthy than in some of the other species. In addition, on ac- 

 count of the large numbers of immature specimens that were 

 present among the adults, only the larger specimens were col- 

 lected, and the sets are scarcely random lots. 



The remarkably discontinuous distribution of D. virgidatus 

 gives rise to the suspicion that it has been introduced into 

 Curasao by commerce ; it is noteworthy that this species also 

 occurs in St. Martin and St. Eustatius, two of the islands of 

 the northern Lesser Antilles, which are also part of the Nether- 

 lands Colony of Curagao (c/. Vernhout, I. c, p. 184). 



