WEST AMERICAN PYRAMTDELLID MOLLUSKS. 163 



timate and penultimate turns they become somewhat enfeebled from 

 the middle of the whorl between the sutures to the periphery. 

 There are about 16 of these ribs on the first, 18 on the third, 20 

 upon the fourth, and 22 upon the penultimate turn. The intersec- 

 tions of the ribs and spiral keels form low elongated tubercles, the 

 long axis of which coincides with the spiral sculpture. The meshes 

 inclosed b}" the keels and ribs are deeply impressed squarish pits. 

 Periphery and base of the last whorl well rounded, the latter somewhat 

 inflated and marked by six spiral cords, which are successively 

 closer spaced and a little less strongly developed from the periphery 

 to the umbilical area. The channels between the cords are crossed 

 by many very slender raised vertical threads. Aperture oval, 

 slightly effuse anterior!}- outer lip thin; columella reenforced on its 

 posterior two-thirds by the attenuated base, free and somewhat 

 revolute anteriorly ; parietal wall glazed by a thin callus. 



The type has six post-nuclear whorls and measures: Length 3.3 

 mm., diameter 1.2 mm. It and nine additional specimens are Cat. 

 no. 107690, U.S.N.M., and were collected by Dr. C. F. Newcombe 

 at Cumshewa Inlet, Queen Charlotte Island, British Columbia, in 10 

 fathoms. Two other lots of one specimen each come from Monterey, 

 Cat. no. 73998, U.S.N.M., in the Stearns collection, and Cat. no. 

 196283, U.S.N.M., collected by Mr. F. L. Button. 



ODOSTOMIA (CHRYSALLIDA) BENTHINA, new name. 



Plate 17, figs. 9, 9a. 



Chrysallida ohlonga Carpenter, Cat. Mazatlan Shells, 1856, pp. 418-19; not 

 Odostomia ohlonga Macgillivray. 1848. 



Shell elongate-conic, white. Nuclear whorls small, deeply obliquely 

 immersed in the first post-nuclear turn, above which onl}' the tilted 

 edge of the last volution projects. Post-nuclear whorls well rounded, 

 marked by slender, nodulous, retractive axial ribs, which terminate 

 at the posterior extremity of the supra-peripheral cord, leaving this 

 smooth. Of these ribs about 35 occur upon the first whorl, 28 upon 

 the second and third, 22 upon the fourth, and 26 upon the penultimate 

 turn. In addition to the axial ribs, the whorls are marked by five 

 strong, spiral cords, the junction of which with the ribs form tubercles. 

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

 ornamented \\ith seven equal and equally spaced spiral cords, the 

 grooves between which are marked by fine, raised axial threads. 

 Aperture pyriform, somewhat effuse anteriorly; posterior angle acute; 

 outer lip thin, showing the external sculpture witliin; columella 

 slender, curved, and reflected, provided with an oblique fold at its 

 insertion; parietal wall covered with a thin callus. 



Four specimens were taken from Spondylus at ^lazatlan, Mexico. 

 Tablet 1971, Liverpool collection, British Museum, contains the largest 



