no. 1826. MOLLUSKS OF THE GENUS BITTIUM—BARTSCH. 407 



ing, marked on the first whorl by a strong, median keel and a feeble 

 cord halfway between this and the suture, the space between the 

 median keel and the summit forming a strongly sloping shoulder. 

 On the third post-nuclear turn two slender spiral cords appear, 

 one of which is at the summit and the other halfway between this 

 and the median cord. On the fifth whorl an additional spiral cord 

 is intercalated between the two on the shoulder. The cords on the 

 shoulder and also the one anterior to the median grow rapidly in 

 strength until finally, on the last volution, they are practically all 

 equal. In addition to the spiral cords, the whorls are marked by 

 moderately strong, decidedly curved, almost vertical, distant axial 

 ribs. These are quite absent on the early whorls, being first indi- 

 cated on the third post-nuclear turn. On the fourth there are 12, 

 on the fifth to seventh there are 14, on the eighth 18, and on the 

 penultimate turn 20. The intersections of the axial ribs and spiral 

 cords form weak, elongated tubercles; the long axes of which coin- 

 cide with the spiral sculpture, while the spaces inclosed between 

 the two appear as very elongated, narrow pits. Sutures moderately 

 constricted, showing a portion of the peripheral keel. Periphery 

 of the last whorl marked by a keel about as wide as the strong spiral 

 cords between the sutures. Base short, slightly rounded, marked 

 by five spiral cords which decrease in size and spacing from the 

 periphery to the umbilical area. Aperture subquadrate, chan- 

 neled anteriorly; posterior angle obtuse; outer lip thin, showing the 

 external sculpture within, sinuous at the edge; columella moder- 

 ately strong, oblique, somewhat twisted, and reflected; parietal wall 

 glazed with a thin callus. 



The type and 4 specimens (Cat. No. 96899, U.S.N.M.) were 

 dredged at U. S. Bureau of Fisheries station No. 2828, in 10 fathoms, 

 on shell bottom, off Cerralvo Island, Gulf of California. The type 

 has nine and one-half post-nuclear whorls and measures: Length 

 7.9 mm., diameter 2.8 mm. 



BITTIUM (SEMIBITTIUM) LARUM, new species. 



Plate 57, fig. 4. 



Shell very regularly elongate-conic, light brown. Nuclear whorls 

 at least two, worn. Post-nuclear whorls appressed at the summit, 

 decidedly overhanging. The early post-nuclear whorls are marked 

 by four equal and equally spaced spiral cords, the first of which is at 

 the summit; these cords divide the space between the sutures into 

 four equal parts. On the sixth whorl intercalated spiral cords make 

 their appearance in the middle, between all the primary cords; these 

 attain a little more than half the strength of the primary cords on the 

 last turn. In addition to the spiral sculpture, the whorls are marked 

 by moderately strong, almost vertical, axial ribs, of which 14 occur 



