WEST AMERICAN PYRAMIDELLID MOLLUSKS. 141 



The type (Cat. no. 206894, U.S.N.M.) comes from the Bay of 

 Panama. It has seven post-nuclear whorls and measures: Length 

 3.3 mm., diameter 1.3 mm. 



ODOSTOMIA (CHRYSALLIDA) ACRYBIA, new species. 

 Plate 14, fig. 6. 



Shell elongate-conic, milk-white. (Nuclear whorls decollated.) 

 Post-nuclear whorls very slightly rounded, somewhat contracted at 

 the sutures, feebly shouldered at the summits, marked by strong, 

 almost vertical axial ribs, of which 14 occur upon the second, 16 upon 

 the third, 18 upon the fourth, 20 upon the fifth, and 22 upon the 

 penultimate turn. Intercostal spaces a little wider than the ribs, 

 crossed by four slender spiral cords, the junction of which with the 

 ribs renders them feebly nodulous. Sutures strongly impressed but 

 not channeled. Periphery and base of the last whorl well rounded, 

 the latter marked by nine slender spiral cords, the spaces between 

 which are crossed by fine axial threads. Aperture oval, slightly 

 effuse anteriorly; posterior angle acute; outer lip thin, showing the 

 external sculpture within; columella twisted, decidedly reflected ante- 

 riorly, provided with a strong fold at its insertion; parietal wall 

 covered with a thick callus. 



The type (Cat. no. 206895, U.S.N.M.) comes from Point Abreojos, 

 Lower California. It has seven post-nuclear whorls and measures: 

 Length 3.2 mm., diameter 1 .2 mm. Another specimen from the same 

 locality is in Mr. Hemphill's collection. 



ODOSTOMIA (CHRYSALLIDA) COMMUNIS C. B. Adams. 



Plate 14, figs. 10, 10a. 



Chemnitzia communis C. B. Adams, Ann. Lye. Nat. Hist, of N. Y., vol. 5, 1852, 

 p. 390. 



Shell conic, vitreous to milk-white. Nuclear whorls at least two, 

 forming a depressed helicoid spire, whose axis is at right angles to 

 that of the succeeding turns, in the first of which it is about one-half 

 immersed. Post-nuclear whorls flattened, strongly contracted at the 

 suture and decidedly shouldered at the summit, marked by strong 

 vertical axial ribs of which there are 16 upon the first and second, 

 18 upon the third to fifth, and 20 upon the penultimate turn. In 

 addition to the ribs the whorls are marked by four spiral cords about 

 one-half as strong as the ribs, between the sutures; the first of these 

 is at the angle of the shoulder. The junction of the spiral cords 

 and ribs nodulous; the spaces inclosed between them rectangular 

 pits. Sutures channeled. Periphery of the last whorl marked by a 

 spiral cord at whose posterior margin the axial ribs terminate. Base 

 produced, moderately rounded, marked by ten spiral cords, which, 

 like the grooves separating them, decrease regularly in size from the 



