WEST AMERICAN PYRAMIDELLID MOLLUSKS. 81 



one and three-fourths, moderately large, depressed, helicoid, havmg 

 their axis at right angles to that of the succeeding turns, in the first 

 of which they are about one-fourth immersed. Post-nuclear whorls 

 well rounded, the strongest convexity falling a little anterior to the 

 middle between the sutures, appressed at the summit, marked by 

 strong, sublamellar, slightly protractive axial ribs, of which 16 occur 

 upon the first to seventh whorl, 18 upon the eighth, 20 upon the ninth 

 and the penultimate turn. Intercostal spaces about three times as 

 wide as the ribs, shallow, marked by a series of deep spiral pits, at 

 the periphery and another a little posterior to the middle of the 

 whorls. The space between the peripheral and the median pits is 

 crossed by ten unequal and unequally spaced, fine spiral striations. 

 The space between the median row of pits and the summit is crossed 

 by ten incised spiral lines of similar character. Sutures well 

 impressed. Periphery of the last whorl slightly angulated. Base 

 short, well rounded, marked by about thirteen fine, well incised, 

 equal and equally spaced spiral striations. Aperture rhomboid; 

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

 within; columella straight, oblique and revolute, provided with a 

 weak fold at its insertion. 



The type (Cat. no. 163261, U.S.N.M.) has eleven post-nuclear 

 whorls and measures: Length 6.5 mm., diameter 1.6. mm. It and 

 two additional specimens were dredged at U. S. Bureau of Fisheries 

 station 2822, in 21 fathoms, gray sand and broken shells, off La 

 Paz, Lower California. 



TURBONILLA (PYRGISCUS) PLUTO, new species. 

 Plate 9, fig. 9. 



Shell very robust, chestnut brown. (Nuclear whorls decollated.) 

 Post-nuclear whorls flattened, moderately shouldered at the summit 

 and scarcely at all contracted at the sutures, marked by rather 

 irregular, low, rounded, variously slanting axial ribs which are 

 completely eroded on the first four whorls, on the fifth and sixth 

 there are 24, on the seventh and the penultimate there are 38. Inter- 

 costal spaces a little narrower than the ribs, marked by four spiral 

 series of broad strongly impressed spiral pits, on the anterior two- 

 thirds of the whorls between the sutures ; the posterior third is marked 

 by two closely spaced, well incised, strong spiral lines, the first of 

 which is about as far posterior to the neighboring pit as the space 

 which separates that from its fellow. Both spiral pits and lines cut 

 strongly into the sides of the ribs and pass feebly over their summits, 

 rendering them somewhat tuberculate. Sutures well impressed. 

 Periphery of the last whorl marked by a plain band, well rounded. 

 Base moderately long, well rounded, marked by the very feeble con- 

 tinuations of the axial ribs and six equal and equally spaced, broad 



