92 BULLETIN OF THE 



regular Drillia aperture and nucleus, and it is therefore referred to that genua. 

 The curvature and number of the ribs vary slightly, and the spaces between are 

 indifferently perfectly smooth, or finely spirally striate, especially toward the 

 anterior end of the shell. 



This species differs from D. Verrillii, with which it has many points in com- 

 mon, in the absence of the angulation of the ribs at the periphery, the longer 

 and more slender form of both shell and riblets, and in D. Verrillii the absence 

 of any spiral sculpture except the fasciole and a few coarse threads on the 

 canal. These shells are so very small and polished that it is extremely diffi- 

 cult for an artist in pure line-work to represent them adequately. Only lithog- 

 raphy with its delicate mutations of shade can do it properly. For this reason 

 our figures of this species and D. Verrillii are less satisfactory than most of 

 these which represent rougher and larger shells. 



Drillia? Dalli Verriix. 



Pleurotoma Dalli Verrill, Trans. Conn. Acad.,V p. 451, pi. lvii. figs. 1, la, April, 1882. 



Habitat. Variety acloneta, Station 206, near Martinique, in 170 fins., fine 

 sand, temperature 49° F. ; U. S. Fish Commission Station 2668, in 294 fms., 

 gray sand, off Fernandina, Fla., temperature 46°.3. Variety cestrota, Station 

 2399, in 196 fms., mud, in the Gulf of Mexico, between the delta of the Mis- 

 sissippi and Cedar Keys, Fla., temperature 51°. 6. Typical form, off Martha's 

 Vineyard, in 94 to 143 fms., and off Delaware Bay, in 104 fms. 



This species, recognizable by its large blunt tip and brownish livid streaks 

 or tint, is notably variable. The type is obscurely ribbed; on the upper whorls 

 the ribs are a little stronger. The variety which I have called acloneta is 

 totally without ribs, and for this reason the fasciole is less apparent. The 

 variety cestrota, on the other hand, has the ribs much stronger than in the 

 typical form, and closer set; they even undulate the fasciole a little. The three 

 forms of this species, with their connecting varieties, illustrate in a character- 

 istic manner the mutability of these archibenthal species. 



Drillia nucleata Dall. 



Plate XI. Fig. 1. 



Pleurotoma (Drillia) nucleata Dall, Bull. M. C. Z., IX. p. 62, Aug. 12, 1881. 



? Pleurotoma (Drillia) amblia Watson, Journ. Linn. Soc, XVI. p. 249, March, 1882. 



1 Clionella amblia Watson, Chall. Gastr., p. 373, pi. xxii. fig. 12, 1885. 



Habitat. Gulf of Mexico, Station 5, in 229 fms., and Station 43, in 339 

 fms. Antilles, ^ Ccmbrero, in 54 fms., an 1 Station 230, off St. Vincent, in 

 464 fms., ooze. U. S. Fish Commission Station 2644, off Cape Florida, in 

 193 fms., sand, temperature 43°.4 F. 1 Challenger expedition, off Culebra 

 Island, in 390 fms., ooze. 



