WEST AMERICAN PYRAMIDELLID MOLLUSKS. 151 



marked by a spiral groove, crossed b}^ the continuations of the axial 

 ribs, which terminate at the posterior edge of the first basal keel. 

 Base well rounded posteriorly, somewhat attenuated anteriorly, 

 marked by six almost equal spiral keels, which are less developed 

 about the umbilical area. The deep grooves between these keels are 

 crossed by numerous very slender, raised axial threads. Aperture 

 oval; posterior angle obtuse; outer lip thin, shovudng the external 

 sculpture within; rendered decidedly sinuous by the spiral cords; 

 columella moderately strong, decidedly reflected anteriorly, provided 

 with a fold at its insertion. 



The t3^pe (Cat. no. 162765, U.S.N.M.) comes from San Diego, Cali- 

 fornia. It has five post-nuclear whorls and measures: Length 3.5 

 mm., diameter 1.7 mm. Cat. no. 162766, U.S.N.M., one specimen 

 from Whites Point, San Pedro. Cat. no. 168569, U.S.N.M., one 

 specimen from U. S. Bureau of Fisheries station 2932, in 20 fathoms, 

 temperature 58°, off Los Coronados Islands. 



Named for Mrs. T. S. Oldroyd. 



ODOSTOMIA (CHRYSALLIDA) NODOSA Carpenter. 



Plate 15, figs. 9, 9a. 

 Chrysallida nodosa Carpenter, Cat. Mazatlan Shells, 1856, pp. 417, 418. 



Shell very elongate-ovate, white. Nuclear whorls small, deeply 

 obliquely immersed in the first of the succeeding tiu"ns. Post-nuclear 

 whorls moderately rounded, considerably contracted at the sutures 

 and moderately shouldered at the summit, marked by strongly nodu- 

 lous, decidedly retractive axial ribs, of which 14 occur upon the first, 

 16 upon the second to fourth, and 22 upon the penultimate turn. In 

 addition to the axial ribs the w^horls are marked between the sutures 

 by foiu" spiral keels which are a little less strong than the ribs and 

 render them nodulous at their junction. The spaces inclosed between 

 the ribs and spiral cords are oblong oval pits on all the whorls but the 

 last on which they are round. Sutures subchanneled. Periphery of 

 the last whorl marked by a strong broad groove, is curved b}^ the 

 axial ribs which extend to the posterior border of the first basal cord. 

 Base of the last whorl well rounded, marked by six strong rounded, 

 spiral cords which are a little weaker at the umbilical area than at 

 the periphery. Spaces separating the spiral cords of the base about 

 as ^\^de as the cords, covered by numerous slender axial threads. 

 Aperture oval; posterior angle obtuse; outer lip thin, showing the 

 external sculpture ^\'ithin; columella slender, curved, provided \dih. 

 a strong fold at its insertion ; parietal wall covered wath a thin callus. 



Five specimens of this species were taken off Spondylus at Mazatlan, 

 Mexico. Tablet 1969, Liverpool collection, British ]\[useum, contains 

 two specimens ; one of these has six post-nuclear whorls and measures : 

 Length 4.1 mm., diameter 1.8 nmi. 



