no. 1826. MOLLUSES OF THE GENUS BITTIUM— BARTSCH. 393 



the tubercles are truncated on the posterior margin and slope gently 

 anteriorly. Base of the last whorl moderately long, ornamented 

 with seven spiral cords, of which the two immediately below the 

 periphery are the strongest and broadest, while the two bounding 

 the umbilical area are wider than those intervening. Sutures 

 channeled. Aperture irregular, channeled anteriorly; posterior angle 

 obtuse; outer lip thin, sinuous, showing the external sculpture 

 within; columella stout, short, twisted, and reflected; parietal wall 

 glazed with a moderately thick callus. The specimen figured has 

 eight post-nuclear whorls and measures: Length 7.8 mm., diameter 

 2.7 mm. 



Specimens of this species were dredged in 8 to 27 fathoms from 

 Ucluelet to Ship Channel, Barclay Sound, Vancouver Island, British 

 Columbia. Part of these are in the collection of the Dominion Geo- 

 logical Survey, and others are in the U. S. National Museum collection, 

 Cat. No. 211545. 



BITTIUM (SEMIBITTIUM) ATTENUATUM Carpenter. 



Plate 54, figs. 1, 2, and 5. 



Bittium attenuatum Carpenter, Rep. Brit. Ass. Adv. Sci., 1864, p. 655; 

 =Bittium ? var. esuriens Carpenter, Rep. Brit. Ass. Adv. Sei., 1864, p. 655; 

 =Bittium (? var.) esuriens Carpenter, Ann. Mag. Nat. Hist., ser. 3, vol. 15, 1865, 



p. 181; 

 —Bittium (? var.) esuriens Carpenter, Journ. Conch., vol. 12, 1865, p. 242; 

 = Bittium attenuatum Carpenter, Jonrn. Conch., vol. 12, 1865, pp. 242-243. 



Shell elongate-conic, varying in color from plain white to brown, 

 variously banded or maculated. Nuclear whorls two, moderately 

 rounded, smooth. Post-nuclear whorls slightly rounded, ornamented 

 with weak spiral bands which are best developed on the early whorls. 

 These spiral bands are truncated anteriorly and slope gently to the 

 posterior boundary. The early whorls have three spiral bands, of 

 which the posterior, at the summit, is less strongly developed than 

 the other two, which divide the remaining space between the sutures 

 equally. On the middle whorls the posterior keel has a tendency to 

 become divided, while on the later turns it becomes obsolete. In 

 addition to the spiral sculpture, the whorls are marked by poorly 

 developed, rounded, protractive, axial ribs which render their inter- 

 sections with the spiral cords nodulose. Of these ribs, 12 occur upon 

 the third and 14 upon each of the remaining turns upon which ribs 

 are discernible. The spaces inclosed between the ribs and spiral 

 bands are shallow, impressed, rectangular pits. In addition to the 

 axial ribs, the whorls are marked by numerous fine lines of growth. 

 Periphery of the last whorl marked by a spiral band, which is 

 separated from the first band above the periphery by a sulcus as wide 

 as the sulci on the spire. Base short, well rounded, marked by six 



