WEST AMERICAN PYRAMIDELLID MOLLUSKS. T'? 



TURBONILLA (PYRGISCUS) GRACILLIMA Carpenter. 



Plate 7, %. 9. 



Chemnitzia gracillima Carpenter, Cat. Mazatlan Shells, 1856, p. 431; not Tur- 

 bonilla gracillima Gabb, 1865, nor Turbonilla gracillima Koch and Wiech- 

 MANN, 1872, not Turbonilla gracillima Almers and Bopill, 1898. 



Shell very slender, acute, milk-white. Nuclear whorls prolonged, 

 partly lost. Post-nuclear whorls well rounded at first, later flattened, 

 moderately contracted at the periphery and slightly shouldered at the 

 summit, marked by slender, almost vertical, axial ribs, of which 12 

 occur upon the first, 14 upon the second and third, 16 upon the fourth, 

 18 upon the fifth and penultimate turn. Intercostal spaces as broad 

 as the ribs, terminating suddenly at the periphery, crossed by about 

 fourteen equal and equally spaced spiral pits, which are equal to the 

 spaces which separate them. Periphery and base of the last whorl 

 well rounded, without sculpture, smooth. Aperture rhomboidal ; pos- 

 terior angle obtuse; outer lip thin; columella slender, somewhat 

 twisted. 



Two specimens were collected off Chama at Mazatlan, Mexico; the 

 larger of these has eight post-nuclear whorls, and measm-es : Length 3 

 mm., diameter 0.9 mm., and is on tablet 2001, Liverpool collection, 

 British Museum. 



TURBONILLA (PYRGISCUS) VEXATIVA, new species. 

 Plate 7, fig. 11. 



Shell stout, chestnut brown. (Nuclear whorls decollated.) Post- 

 nuclear whorls flattened in the middle, slightly rounded toward the 

 appressed summit, and weakly contracted at the periphery, marked 

 by weak, rounded, vertical axial ribs, which terminate abruptly at the 

 periphery, of which 22 occur upon the fifth, 24 upon the sixth and 

 seventh, and 26 upon the penultimate turn. Intercostal spaces about 

 one and one-half times as wide as the ribs, marked by six equal and 

 equally spaced spiral grooves, which divide the space between the 

 sutures into seven equal parts. Sutiu-es well impressed. Periphery 

 of the last whorl angulated. Base short, marked by eight strongly 

 incised spiral lines, which decrease in spacing from the periphery to 

 the umbilical area. The space immediately behind the columella 

 bears a number of closely spaced, fine, spiral striations. Apertiu"e 

 rhomboidal; posterior angle obtuse; outer lip thin, showing the 

 external markings within; columella slender, somewhat twisted and 

 slightly revolute. 



The type (Cat. no. 160200, U.S.N.M.) was collected by Mr. E. W. 

 Roper at San Pedro, California. It has lost the nucleus. The nine 

 remaining whorls measure: Length 6.2 mm., diameter 2.1 mm. 



