410 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



below the summit and renders this decidedly shouldered. In addi- 

 tion to the spiral keels, the whorls are marked by axial ribs, of which 

 14 occur upon the second, 16 upon the third, 20 upon the fourth, 24 

 upon the fifth and sixth, 26 upon the seventh, and 28 upon the eighth 

 and penultimate turns. The intersections of the axial ribs and the 

 spiral cords form well-rounded tubercles, while the spaces inclosed 

 between them are squarish pits. Sutures strongly constricted. 

 Base of the last whorl rather long, marked by three prominent 

 spiral keels and a fourth slender thread at the columella. Aperture 

 irregular, channeled anteriorly; posterior angle obtuse; outer lip 

 rendered sinuous by the external sculpture; columella short, stout, 

 twisted, and reflected; parietal wall covered with a thick callus. 



The type is on tablet 2034, Liverpool collection, British Museum. 

 It has nine post-nuclear whorls and measures: Length 4 mm., diame- 

 ter 1.3 mm. Our figure is copied from a camera lucida sketch by 

 Doctor Carpenter. 



BITTIUM GIGANTEUM, new species. 

 Plate 55, fig. 2. 



Shell elongate-conic, very large, white. Nuclear whorls decollated. 

 Early post-nuclear whorls with a strongly sloping shoulder, marked 

 by three spiral keels, one of which is at the summit, another median, 

 and the other a little nearer the median than the suture. On the 

 succeeding turns an additional cord makes its appearance, between 

 the one at the summit and the median keel, soon gaining sufficient 

 strength to equal the one at the summit. In addition to these spiral 

 cords, the whorls are marked by strong, well-rounded, curved, 

 retractive, axial ribs, of which 14 occur upon the second, 16 upon 

 the third to fifth, 18 upon the sixth to tenth, and 22 upon the penulti- 

 mate turn. The junctions of the axial ribs and spiral cords form 

 well rounded tubercles, while the spaces inclosed between them are 

 well impressed, squarish pits. On the last two whorls additional 

 spiral cords make their appearance on either side of the median 

 cord. Sutures very strongly impressed. Periphery of the last 

 whorl marked by a channel across which the feeble continuations 

 of the axial ribs extend. Base short, slightly rounded, marked by a 

 cord immediately below the periphery and slender incised lines 

 anterior to this. Aperture moderately large, subquadrate, chan- 

 neled anteriorly; posterior angle obtuse; outer lip rendered sinuous 

 by the external sculpture; columella short, almost straight, and 

 reflected; parietal wall covered with a thick callus. 



The type and additional specimens (Cat. No. 14935, U.S.N.M.) 

 come from the post-Pliocene of San Diego, California. The type 

 has 12 post-nuclear whorls (having lost the nucleus and probably 



