WEST AMERICAN PYEAMIDELLID MOLLUSKS. 121 



KEY TO THE SPECIES OF THE SUBGENUS DIINKERIA. 



Spiral sculpture between the sutures of uniform character. 



Spiral cords between the sutures 7^ sedillina, p. 121. 



Spu-al cords between the sutures 5 or 5^. 



Adult shell more than 6 mm. long Inminata, p. 122. 



Adult shell less than 4 mm. long. 



WTiorls slightly rounded hipolitensis, p. 123. 



Whorls strongly rounded. 

 Shell elongate-ovate. 



Basal cords 5 suhangidata, p. 124. 



Basal cords 6 andrevsi, p. 124. 



Shell elongate-conic exroJpa, p. 123. 



Spiral sculpture between the sutures not of uniform character. 



Adult shell more than 10 mm. long arata, p. 125. 



Adult shell less than 6 mm. long genilda, p. 125. 



TURBONILLA (DUNKERIA) SEDILLINA, new species. 



Plate 12, figs. 3, 3a. 



Shell elongate-conic, milk-white. Nuclear whorls two and one- 

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

 to that of the succeeding turns, in the first of which it is one-fourth 

 mmersed. Post-nuclear whorls flattened in the middle, with a 

 strong sloping shoulder, which extends over the posterior third be- 

 tween the-sutures, appressed at the summit and slightly constricted 

 at the suture, marked by slender, sublamellar, sinuous, almost verti- 

 cal axial ribs, of which 16 occur upon the first three whorls, 18 upon 

 the fourth to sixth, 20 upon the seventh and eighth, and 24 upon the 

 penultimate turn. Intercostal spaces three times as w^ide as the 

 ribs, marked ])y seven rather broad and deeply incised spiral grooves, 

 the interspaces appearing as flattened cords, of which the one be- 

 tween the second and third groove below the summit is at the shoulder 

 and a little broader than the rest. Sutures strongly constricted. 

 Periphery of the last whorl somewhat angulated. Base short, well 

 rounded, marked by seven irregular and irregularly spaced spiral 

 striations. Aperture broadly oval; posterior angle acute; outer lip 

 tliin, showing the external sculpture within; columella slender, and 

 decidBdly curved. 



The t3'pe and nine specimens (Cat. no. 162697 U.S.N.M.) were 

 dredged at U. S. Bureau of Fisheries station 2823, in 26^ fathoms, off 

 La Paz, Gulf of Cahfornia. It has nine post-nuclear whorls and 

 measures: Length 5.3 mm., diameter L4 mm. Cat. no. 206887, 

 U.S.N.M., one specimen at U. S. Bureau of Fisheries station 2822, in 

 21 fathoms, also froiri La Paz. Cat. no. 206888 U.S.N.M., one speci- 

 men, from U. S. Bureau of Fisheries station 2826, 9^ fathoms, off 

 Ceralvo Island, Gulf of C'alifornia. 



