MUSEUM OF COMPARATIVE ZOOLOGY. 89 



dary spiral threads ; all these cross (on the penultimate whorl) fourteen even, 

 rounded, narrow riblets, with narrower interspaces, which start at the anterior 

 edge of the fasciole, cross the whorl, and fail on the canal ; suture distinct, 

 wavy ; fasciole obscure, not excavated ; whorls rounded ; varix stout, thick, 

 and rounded ; aperture narrow, notch strongly marked, round ; outer lip thin, 

 without lirae ; inner lip with a thin, smooth, elevated callus ; canal distinct, 

 rather long and narrow, not recurved;, pillar straight. Lon. of shell, 23.0; of 

 last whorl, 12.5; of aperture, 9.7; max. lat. of shell, 5.5 mm. 



Habitat. Gulf of Mexico, between the delta of the Mississippi and Cedar 

 Keys, Florida, at U. S. Fish Commission Stations 2377, 2399, and 2402, in 

 210, 196, and 111 fms., mud, temperature 52° to 67° F. 



B. Nearly smooth ribbed species. 



Drillia ebur Reeve. 



Pleurotoma ebur Reeve, P. Z. S., 1845, p. 116; Conch. Icon., pi. xxx. fig. 275, Dec, 



1845. 

 Clavus ebur Tryon, Man., VI. p. 188, pi. xiii. fig. 56. 



Habitat. Cape Hatteras to Florida, living, in 14 to 50 fms. Also at Station 

 10, Gulf of Mexico, in 34 fms. ; Station 22, in 95 fms.; Station 36, in 84 fms.; 

 off Sombrero, in 54 fms. ; all specimens dead. 



These shells were probably adventitious in the localities where found by 

 the Blake, having perhaps been disgorged by fishes. 



This species forms a sort of transition to the preceding section. The nucleus 

 is peculiar in being almost entirely sculptured with strong radiating riblets, and 

 a little later with close-set fine spirals. This character varies somewhat in 

 strength, but is sufficiently well marked in all the specimens I have examined 

 to be regarded as characteristic of the species as far as known. 



Drillia fucata Reeve. 



Pleurotoma fucata Reeve, P. Z. S. 1845, p. 110; Conch. Icon., fig. 169. 

 Pleurotoma paria Reeve, Conch. Icon., fig. 334, Jan., 1846. 



Habitat. Coast of North Carolina, off Cape Fear, in 14 fms., sand, to St. 

 Thomas and Haiti. 



This is the variety with numerous (about 16) ribs, which is the typical 

 form. This species in all its forms is larger than D. ebur Reeve, and has the 

 usual smooth, vitreous Drillia nucleus ; it is proportionally shorter and has the 

 last whorl stouter than any of its near connections. It is covered with fine 

 spiral threading, which in well developed specimens is beautifully reticulated 

 by very close, fine, sharp, elevated incremental lines, visible in the interspaces. 

 The number and stoutness of the ribs varies greatly. There are specimens 

 without any ribs; I have one from Samana Bay, Santo Domingo. The variety 

 paria Reeve has six or eight ribs, is pale colored, and ranges from the West 

 Indies to Cape Fear, North Carolina. 



