270 CALIFORNIA ACADEMY OF SCIENCES. 



The species of this genus are distributed in all seas. All our West American 

 forms have the columellar fold internal and hardly to be seen without breaking away 

 part of the whorls. 



The number of species is so great, and they are so .similar to one another, that 

 a number of sections, based chiefly on the types of scidpture, have been found con- 

 venient in treating of them. Most of these sections grade into one another through 

 peripheral species. 



Section atrioturhoiiillu Sacco. 



Sttiol7irbo7iilla ShCCO, I. Moll, del Piedmonte e della Liguria, p. 94, 1892. 



Shell as in Chemnitzia, but very finely and closely spirally striated on the spire and base. 



Type, Strioturhonilla alpina Sacco, I. c. 



284. Turbonilla (Strioturbonilla) muricata Carpenter. 



Chemnitzia muricata Cpr., Mazatlan Cat., Brit. Assn. Rept., 1856, p. 260. 



Shell small, slender, solid, rather thin, milk-white; nuclear whorls two and one-half, heli- 

 coid, smooth, one-third sunken, their axis being at right angles to the a.xis of the post-nuclear 

 whorls; post-nuclear whorls flattened, ornamented by eighteen to twenty-two very prominent, 

 elevated, convex-topped, slightly oblique axial ribs, which extend to the suture posteriorly, but fuse 

 just before reaching the suture anteriorly; ribs on body-whorl fuse abruptly at angle; the intercostal 

 spaces appear as deep channels about as wide as the ribs; the suture appears very distinct, owing to 

 a sharp angulation on the upper part of the whorl, and a slight contraction at the base; body-whorl 

 rather short, rounded, smooth on base, except for fine, incremental lines; aperture subquadrate, the 

 outer lip meeting the columella at almost right angles. 



Dimensions. — Long. 5.4 mm.; lat. 1.3 mm.; altitude of body-whorl, 1.7 mm. 



This species resembles T. stearnsii, but may be distinguished from that species 

 by more elevated, narrower and more numerous ribs and by the stronger angulation 

 above. The specimen examined lacked prominent spiral sculpture as far as the 

 writer was able to determine. This specimen was identified by Dr. Dall, but the 

 species was omitted from the text prepared by Dall and Bartsch. 



Rather common in the up])er San Pedro series of San Pedro and LosCerritos; 

 rare in the lower San Pedro series at Deadman Island and San Pedi'O. 



Living. — Gulf of California to Mazatlan (Carpenter). 



Pleistocene. — San Pedro (Arnold). 



285. Turbonilla (Strioturbonilla) similis C. B. Adains. 



Chemnitzia similis C. B. Ads., Catalogue Panama Shells, No. 228, Ann. N. Y. Lye. Nat. Hist., 

 Vol. V, 1852, p. 392. 



Shell small, slender, solid, milk-white, thick; nuclear whorls two and one-half, smooth, 

 helicoid, about one-third sunken, their axis being at right angles to the axis of the post- 

 nuclear whorls; post-nuclear whorls nine, somewhat flattened, ornamented by fourteen to eighteen 

 prominent, broad, convex, oblique, axial ribs, which traverse nearly the whole of the exposed 



