no. 1826. MOLLU&KH OF TUB GENUS B ITT IV M— BART UGH. 397 



BITTIUM (SEMIBITTIUM) RUGATUM Carpenter. 



Plate 56, figa. 4 and 5. 



Bittium rugatum Carpenter, Ann. Mag. Nat. Hist., ser. 3, vol. 17, 1866, p. 276; 

 =Bittium asperum Carpenter, not Gabb, Ann. Mag. Nat. Hist., ser. 3, vol. 17, 

 1866, p. 276. 



Shell elongate-conic, white. Nuclear whorls a little more than 

 one, well rounded, smooth. Post-nuclear whorls appressed at the 

 summit, decidedly overhanging, the early ones marked by two strong 

 spiral cords on the anterior half between the sutures, and a third 

 less strongly developed cord at the summit. On the third whorl a 

 fourth spiral makes its appearance between the one at the summit 

 and its neighbor; this fourth spiral soon increases in size, so that on 

 the middle of the shell all four cords are practically of equal strength 

 and spacing. On the last whorl a slender, intercalated cord appears 

 between the anterior two. In addition to the spiral sculpture, the 

 whorls are marked by strong, well-rounded, axial ribs, which are 

 merely indicated on the first two whorls; on the third to sixth turn 

 there are 14, on the seventh there are 16, on the eighth 18, and on the 

 penultimate whorl there are 24. The intersections of the axial ribs 

 and spiral cords form elongated tubercles which have their long axes 

 parallel with the spiral sculpture. The spaces between the spiral 

 cords and axial ribs are elongated, squarish pits. Sutures strongly 

 constricted. Periphery of the last whorl marked by a channel which 

 bears a slender cord. Base well rounded, marked by six spiral cords 

 which grow successively weaker and more closely spaced from the 

 periphery to the umbilical area. Aperture oval, channeled ante- 

 riorly; posterior angle acute; outer lip thin, rendered sinuous by the 

 external sculpture; columella short, twisted, and reflected. 



The specimen described and figured has ten post-nuclear whorls 

 and measures: Length 10.5 mm., diameter 3.5 mm. It is one of 

 six specimens (Cat. No. 7971, U.S.N.M.) from the post-Pliocene of 

 Santa Barbara, California. Doctor Carpenter's type (Cat. No. 7154, 

 U.S.N.M.) does not quite represent the norm of this species, the 

 spiral cord at the summit being only feebly developed on the later 

 turns and the basal sculpture being less strong than usual. 



