WEST AMERICAN PYRAMIDELLID MOLLUSKS. 



161 



strength, of which 4 occur upon the first and second, 5 upon the third, 

 6 upon the fourth and the penultimate wliorl. Of these spiral ridges 

 the second one below the summit is the strongest and marks the angle 

 of the shoulder. The junction of the ribs and cords form feeble 

 nodules best sho\^^l at the shoulder. Sutures strongly constricted. 

 Periphery of the last whorl marked by a low cord. Base well rounded, 

 marked by four low, broad cords and seven exceedingly fine incised 

 lines, the latter about the umbilical area. The narrow, strongly 

 incised grooves which separate the cords are crossed by numerous 

 fine axial tlireads, which give them a pitted appearance. Aperture 

 oval, slightly effuse anteriorly; posterior angle acute; outer lip 

 rendered slightly wavy by the external cords, thin, showing the 

 external sculpture within; columella slender, curved, provided with 

 a deep-seated fold at its insertion. 



The type and ten specimens (Cat. no. 46152, U.S.N.M) come from 

 Todos Santos Bay, Lower California. The type has six post-nuclear 

 whorls and measures: Length 3 nnn., diameter 1.1 mm. 



This is the most variable and the most abundant member of the 

 subgenus Chrysallida. On some the axial ribs extend only over the 

 first two cords below the summit, on others they extend strongly over 

 the periphery and part of the base. The spiral cords also vary in 

 number and strength. The general form, however, seems quite 

 constant. 



The following specimens have been examined: 



ODOSTOMIA (CHRYSALLIDA) DEFOLINIA, new name. 



Plate 17, fig. 5. 



Noemia angusta de Folin, Fonds de la Mer, vol. 2, 1872, p. 165, pi. 6, fig. 7; not 

 Chrysallida angusta Carpenter, 1864. 



Shell conic, crystalline, sliining. Nuclear whorls one and one-half, 

 the greater part immersed in the first of the succeeding turns. Post- 

 nuclear whorls flattened, marked by four spiral ridges between the 

 sutures and axial ribs, the intersections of which form low squarish 

 tubercles of which about 1 i occur upon the second and IS upon 

 the penultimate whorl. Suture poorly impressed. Periphery of the 



