WEST AMEEICAN PYKAMIDELLID MOLLUSKS. 175 



summit, and stronf:;ly contracted at the perij)heiy, marked by strong 

 lamellar ribs, of which 12 occur upon the first, 14 upon the second, 

 and 16 upon the penultimate turn. In addition to the axial ribs the 

 whorls are marked by six strong spiral cords, one of which is at the 

 angle of the shoulder and another at the periphery, the third falls a 

 little anterior to the suture, while the other three divide the remainder 

 of the base into four almost equal parts. Aperture oval, posterior 

 angle obtuse; outer lip thin, rendered angulated by the spiral cords; 

 columella slender, curved, and somewdiat revolute, provided with 

 an oblique fold at its insertion; parietal wall covered with a strong 

 callus. 



Two specimens were taken off Spondylus, at Mazatlan, Mexico. 

 The finest of these is on tablet 1963, Liverpool collection, British 

 Museum. It has four post-nuclear whorls and measures: Length 

 1.8 mm., diameter 0.6 mm. 



ODOSTOMIA (IVIDELLA) ORARIANA, new name. 



Plate 18, fig. 12. 



Cingula (?) turrita C. B. Adams, Ann. Lye. Nat. Hist, of N. Y., 1852, pp. 406, 407; 

 mit Odostomia turrita Hanley, 1844. 



Shell elongate, conic, turreted; milk-white. Nuclear whorls deeply 

 obliquely immersed in the first of the succeeding turns, above which 

 only the tilted edge of the last volution projects. Post-nuclear whorls 

 strongly tabulately shouldered at the summit, flat in the middle, 

 sloping suddenly toward the suture; ornamented b}^ slender axial 

 ribs, of which 15 occur upon the second and 18 upon the remaining 

 whorls. In addition to the axial ribs, the wdiorls are marked between 

 the sutures by two strong spiral keels, one of which is situated at the 

 angle of the shoulder, the other at the posterior termination of the 

 anterior third between the sutures. The junctions of the axial ribs 

 and spiral keels are very slightly nodulous. Sutures deeply chan- 

 neled. Periphery of the last whorl well rounded, marked by a spiral 

 keel. Base w^ell rounded, marked by two spiral keels, which divide 

 the space betw^een the peripheral keel and the umbilical area into 

 three equal })arts, and the continuation of the axial ribs, which are 

 fainter on the base than on the spire. Aperture ovate; posterior 

 angle obtuse; outer lip thin, rendered angular by the keels; columella 

 slender, decidedly curved, reenforced by the base; parietal wall cov- 

 ered with a thin callus. 



The type, which is at Amherst College, was collected by Prof. C. B. 

 Adams at Panama. It has six post-nuclear whorls and measures: 

 Length 2 mm., diameter 0.8 mm. 



