360 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



what shouldered; the third is about as far posterior to the suture as 

 it is removed from the median, while the second is halfway between 

 the first and third. The spaces between the spiral cords are equal 

 and about one and one-half times as wide as the cords. In addition 

 to the spiral sculpture, the whorls are marked by well-rounded, 

 slender, protractive, axial ribs which are almost equal to the spiral 

 cords in strength. Of these ribs, 16 occur upon the first, 18 upon the 

 second to fourth, 20 upon the fifth and sixth, and 24 upon the penulti- 

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

 moderately strong, rounded tubercles, while the spaces inclosed 

 between them are rectangular pits having their long axes parallel 

 with the spiral sculpture. Periphery of the last whorl marked by a 

 strong, spiral cord which is separated from the supraperipheral cord 

 by a channel as wide as that which separates the supraperipheral cord 

 from the median and, like it, is crossed by the axial ribs which ter- 

 minate at the posterior edge of the peripheral cord. Base veiy long, 

 concave, marked by incremental lines and a single, obsolete fasciole 

 a little posterior to the insertion of the columella. Aperture irregu- 

 larly oval; posterior angle very obtuse; outer lip thin, showing the 

 external sculpture within by transmitted light, rendered sinuous at 

 the edge by the external sculpture; columella long, curved and 

 twisted, the edge reflected; parietal wall glazed with a thick callus. 

 The type and another specimen (Cat. No. 213302, U.S.N.M.) were 

 dredged by the U. S. Bureau of Fisheries steamer Albatross at station 

 3566 in 3 fathoms on sand and shell bottom, bottom temperature 58°, 

 in San Diego Bay, California. The type has lost the early nuclear 

 whorls, only a portion of the last remaining. It has eight post- 

 nuclear whorls and measures: Length 4.3 mm., diameter 1.5 mm. 



CERITHIOPSIS WILLIAMSONI Arnold. 



Plato 39, fig. G. 



Bittium williamsoni Arnold, Mem. California Acad. Sci , vol. 3, 1903, p. 295, pi. 

 6, fig. 11. 



Shell minute, elongate-ovate. Post-nuclear whorls ornamented 

 with three spiral cords, of which the first, which is the weakest, is at 

 the summit; the second is considerably nearer to the one at the 

 summit than the third, which is about halfway between the second 

 and the suture. In addition to the spiral sculpture, the whorls are 

 marked with slender, almost vertical, axial ribs, of which about 16 

 occur upon the first and second, 18 upon the third, 20 upon the 

 fourth, and 22 upon the penultimate whorl. The junctions of the 

 axial ribs and spiral cords form well-rounded tubercles, those on the 

 median cord appearing somewhat truncated anteriorly and poste- 

 riorly. The spaces inclosed between the spiral cords and axial ribs 

 are squarish pits. Sutures moderately constricted, showing the pos- 



