WEST AMERICAN PYRAMIDELLID MOLLUSKS. 169 



ODOSTOMIA (CHRYSALLIDA) DECEPTRIX, new species. 



Plate 17, fig. 1. 



Shell ovate, white. Nuclear whorls smooth, deeply obliquely 

 immersed in the first of the succeeding turns, above which only the 

 tilted edge of the last volution projects. Post-nuclear whorls some- 

 what inflated, constricted at the sutures and feebly shouldered at the 

 summits, marked by four equal well incised, spiral lines between the 

 sutures and numerous very retractive lines of growth, with a few 

 feeble indications of axial ribs, at and near the summit, which renders 

 the first and sonfietimes the second space between the incised lines 

 below the summit feebly nodulous. Suture strongly impressed. 

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

 marked by seven incised spiral lines, wliich decrease regularly in 

 spacing from the periphery to the umbilical area. Aperture broadly 

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

 sculpture within; columella quite strong, strongly curved, provided 

 with a strong fold at its insertion; parietal well glazed with a thin 

 callus. 



The type and four specimens (Cat. no. 206904, U.S.N.M.) comes 

 from San Plipolito Point, Lower California. The type has five post- 

 nuclear whorls and measures: Length 2.8 mm., diameter 1.3 mm. 

 Cat. no. 206905, U.S.N.M., contains three specimens from Point 

 Abreojos, Lower California. 



Subgenus PYRGULINA A. Adams. 

 PyrguUna A. Adams, Journ. Linn. Soc. Loudon (Zool.), 1863, p. 4. 



Shell with strong axial ribs wliich extend from the summit to the 

 umbilical area; intercostal spaces of spire and base marked by fine 

 incised spiral lines — not raised threads. 



Type. — Clirysallida casta A. Adams. 



ODOSTOMIA (PYRGULINA) MARGINATA C. B. Adams. 



Plate 18, figs. 5, 5«. 



Chemiiilzia mar(/inata ('. B. Adams, Ann. Lye. Nat. Hist, of N. Y., vol. 5, 1852, 

 pp. 391, 392. 



Shell small, elongate-conic, rather stout, semitranslucent. Nuclear 

 wliorls small, 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 wliich it is about one-fourth immersed. Post-nuclear whorls 

 flattened, moderately contracted at the sutures and sUghtly shoul- 

 dered at the summit, marked by very strong, lamellar, somewhat 

 retractive axial ribs, of winch 14 occur upon all of the whorls. The 

 termination of these ribs form cusps at the summits. Intercostal 

 spaces four times as wide as the ribs, marked by six equal and equally 



