182 BULLETIN 68, UNITED STATES NATIONAL MUSEUM. 



ODOSTOMIA (lOLiEA) AMIANTA Dall and Bartsch. 

 Plate 20, figs. 8, 8a. 



Odostomin (lohra) amianta Dall and Bartsch, Proc. U. S. Nat. Miis., vol. 33, 

 1907, p. 519, pi. 46, figs. 9, 9a. 



Shell broadly conic, yellowish-white. Nucleus small, of two whorls 

 which increase extremely rapidly in size and are obliquely placed. 

 Post-nuclear whorls very strongly shouldered, marked by three very 

 strong lamellar spiral keels on the first and second and four on the 

 succeeding whorls between the sutures. The posterior keel marks the 

 limit of the broad, sloping shoulder and is much the strongest. It 

 is also placed a little farther apart from the next spiral keel than that 

 is from its anterior neighbor. Base of the last whorl well rounded; 

 ornamented by eight spiral ridges, which are less elevated and much 

 more closely and regularly spaced than those between the sutures. 

 The peripheral groove is about ec[ual in width to the one anterior to 

 the posterior keel. The entire shell is marked by fine, sublamellar, 

 regularly spaced, retractive axial ribs, which render the spiral keels 

 somewhat crenulated at their meeting pomts and break the spaces 

 between them into small squares or oblongs. These riblets extend 

 from the sutures to the small umbilicus. Aperture subovate, poste- 

 rior angle obtuse; outer lip thin, somewhat wavy, showing the 

 external sculpture within; columella moderately stout, somewhat 

 curved and strongly revolute, having an oblique fold near its insertion 

 which is barely visible when the aperture is viewed squarely; parietal 

 wall covered by a fairly thick callus. 



The type and another specimen (Cat. no. 105483, U.S.N.M.) were 

 collected at Point Abreojos, Lower California, by Mr. Henry Hemp- 

 hill. It has six post-nuclear whorls and measures: Length 4.4 mm., 

 diameter 2.3 mm. 



The following specimens have been examined : 



