WEST AMERICAN PYRAMIDELLID MOLLUSKS. 



89 



there are many microscopic lines of growth and microscopic spiral 

 striations. Sutures well marked. Periphery of the last whorl some- 

 what angulated, marked by the feeble extensions of the axial ribs. 

 Base short, well rounded, smooth, excepting the fine lines of growth 

 and exceedingly fine, weakly incised spiral striations, among which 

 about nine equal and equally spaced are a trifle stronger than the 

 rest. Aperture rhomboid; outer lip thin, showing the external sculp- 

 ture within; columella moderately strong and slightly revolute. 



The above description is based on two cotypes (Cat. no. 168866, 

 U.S.N.M.). This has furnished the description of the adult shell. 

 It has lost the nucleus and first post-nuclear whorl. The ten remain- 

 ing measure: Length 6.9 mm., diameter 2.2 mm. The other is 

 a young individual and has served for the description of the nucleus 

 and first post-nuclear whorl. These were dredged at U. S. Bureau 

 of Fisheries, station 2901, ofl^ Santa Rosa Island, California. 



The following specimens have been examined : 



TURBONILLA (PYRGISCUS) FLAVESCENS Carpenter. 



Plate 8, fig. 9. 

 Chemnitzia flavescens Carpenter, Cat. Maz. Shells, 1856, p. 432. 



Shell slender, yellowish. Nuclear whorls two and one-half, form- 

 ing a helicoid spire, whose axis is at right angles to that of the suc- 

 ceeding turns, in the first of which it is about one-fourth immersed. 

 Post-nuclear whorls at first well rounded, later flattened, marked 

 by slender, somewhat curved, almost vertical axial ribs, of which 

 18 occur upon the first, 20 upon the second, 22 upon the third and 

 remaining whorls. Intercostal spaces about twice as wdde as the 

 ribs, marked by numerous fine, closely spaced spiral striations. 

 Periphery and base of the last wdiorl well rounded, marked by the 

 feeble continuations of the axial ribs, and many fine spiral striations. 

 Aperture oval; posterior angle acute; outer lip thin; columella slen- 

 der, strongly curved. 



The single specimen of this shell known is on tablet 2003, Havre 

 collection, British Museum, and was taken from a specimen of Spon- 

 dylus calcifer at Mazatlan, Mexico. It has six post-nuclear whorls, 

 the aperture being badly broken, and measures: Length 2.75 mm., 

 diameter 0.8 mm. 



