132 BULLETIN 68, UNITED STATES NATIONAL MUSEUM. 



Post-nuclear whorls sculptured similarly throughout — Continued. 

 Varices absent — Continued. 



Axial ribs present — Continued. 



Axial ribs feeble, usually only indicated near the summit of the whorls. 

 Spiral sculpture consisting of several strong, broad cords, one or more 



of the posterior of which are crenulated . , Miralda, p. 176. 



Spiral sculpture consisting of many subequal lirations. 



Whorls tabulated at the summit Ivara, p. 179. 



Whorls not tabulated at the summit Evalina, p. 180. 



Axial sculpture reduced to mere lirations, frequently only present 

 between the spiral cords. 



Shell umbilicated loUva, p. 181. 



Shell not umbilicated Menestho, p. 184. 



Axial sculpture represented by lines of growth only. 



Spiral markings consisting of well incised lines Evalea, p. 192. 



Spiral markings consisting of many fine wavy striations, 



Amaura, p. 218. 

 Spiral sculpture consisting of a strong peripheral keel, 



Scalenostoma, j). 229. 

 Spiral sculpture absent. 



Aperture rissoid I Heida, p. 231. 



Aperture not rissoid Odostomia, p. 231. 



Subgenus LYSACME Dall and Bartsch. 

 Lysacme D ALL &nd Bartsch, Proc. Biol. Soc. Wash., vol. 17, 1904, p. 14. 



Early post-nuclear whorls loosely coiled, plain, later ones closely 

 coiled with a spiral keel at the periphery and another at the summit 

 of the whorl; base spirally Urate. 



Tyjje. — Ohrysallida clausiliformis Carpenter. 



ODOSTOMIA (LYSACME) CLAUSILIFORMIS Carpenter. 



Plate 13, fig. 2. 



?? Chrysallida clausiliformis Carpenter, Cat. Mazatlan Shells, 1856, p. 426. 



Shell clausiliform. Nuclear whorls two, forming a depressed heli- 

 coid spire, whose axis is at right angles to that of the succeeding 

 turns, in the first of which i't is scarcely at all immersed. First two 

 and one-half post-nuclear whorls loosely coiled, strongly rounded, 

 smooth, separated by very strongly impressed sutiues. Remaining 

 whorls moderately rounded, with a strong spiral cord at the summit 

 and another at the peripher}^, the two being closely appressed at the 

 sutures. Base prolonged, marked by low spiral cords. Aperture 

 irregularly oblong, decidedly effuse anteriorly; columella provided 

 with a strong fold at its insertion. Operculum paucispiral. 



Four specimens were taken off CJiama at Mazatlan, of which the 

 best preservea is on tablet 1987, Liverpool collection, British Museum, 

 which has seven post-nuclear whorls and measures: Length 3.8 mm., 

 diameter 0.9 mm. 



