140 BULLETIN 68, UNITED STATES NATIONAL MUSEUM. 



shouldered at the summit, marked by strong, vertical, axial ribs, of 

 which 18 occur upon the first, 22 upon the second, 20 upon the thhd, 

 22 upon the fourth and penultimate turn. In addition to the axial 

 ribs the whorls are marked by four slender, spiral cords which do not 

 render the ribs tuberculate. The spaces between the cords and the 

 ribs are deep round pits. Sutures channeled. Periphery of the 

 last whorl marked by a groove. Base somewhat attenuated anteri- 

 orly, well rounded posteriorly, marked by seven spiral cords which 

 become somewhat diminished in size from the periphery to the 

 umbilical region. Grooves separating the cords marked by numer- 

 ous slender axial threads. Aperture irregularly pyriform, effuse 

 anteriorly; posterior angle acute; outer lip tliin, showing the exter- 

 nal sculpture within; columella moderately stout, reflected, reen- 

 forced by the base, provided with a fold at its insertion; parietal 

 wall covered with a thin callus. 



Ten specimens (mostly young) off Chama and Spondylus, Liver- 

 pool collection, British Museum, were taken at Mazatlan, Mexico. 

 Tablet 1978 contains three specimens, the largest of which has six 

 post-nuclear whorls and measures: Length 3.1 mm., diameter 0.9 mm. 



ODOSTOMIA (CHRYSALLIDA) EXCELS A, new species. 



Plate 14, fig. 11. 



Shell broadly conic, white. Nuclear whorls smooth, almost com- 

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

 which the tilted edge of the last whorl only projects. Post-nuclear 

 whorls flattened, strongly contracted at the sutures and somewhat 

 shouldered at the summit, marked by strong protractive axial ribs, 

 of which 16 occur upon the second, 18 upon the third, and 20 upon 

 the remaining turns. In addition to the axial ribs the whorls are 

 marked by four slender spiral cords between the sutures, which 

 render the ribs tuberculate at their junction, the spaces inclosed 

 by the ribs and spiral cords are deep, quadrangular pits, the long 

 axis of which coincides with the spiral cords. Periphery of the last 

 whorl marked by a strong sulcus which is crossed by the continuation 

 of the axial ribs. Base of the last whorl attenuated, well rounded, 

 marked by eight subequal and subequally spaced low spiral cords, 

 the grooves between which are crossed by many slender axial threads. 

 The summit of the last whorl falls below the first basal keel and 

 leaves this in the suture. On the last half of the last turn, an addi- 

 tional slender spiral thread divides the space between the first and 

 second and second and third strong spiral cords. Aperture pyriform, 

 somewhat effuse anteriorly; posterior angle obtuse; outer lip (frac- 

 tured), thin, showing the external sculpture within; columella strong, 

 curved, decidedly reflected over the reenforcing base, provided with 

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

 callus which renders the peritreme complete. 



