WEST AMERICAN PYRAMIDELLID MOLLUSKS. 177 



ODOSTOMIA (MIRALDA) ARMATA Carpenter. 



Plate 19, %. 6. 

 Parthenia armata Carpenter, Cat. Mazatlan Shells, 1856, p. 415. 



Shell elongate-conic, white. Nuclear whorls two, deeply, ob- 

 liquely immersed in the first of the succeeding turns. Post-nuclear 

 whorls marked by two strongly elevated tuberculate keels between 

 the sutures, the posterior one of wliich is about twice as wide as 

 its neighbor. Of the crenulations about 20 appear upon the second 

 and third, 22 upon the fourth, and 24 upon the penultimate turn. 

 Sutures strongly channeled. The periphery is marked by a slender 

 keel, while the base has two a little weaker than the peripheral one 

 wliich divides the space between this and the umbihcal area into 

 three equal parts. Aperture ovate; outer lip thin; columella rather 

 thick, reflected and provided with a slender fold at its insertion; 

 parietal wall provided ynt\\ a thin callus. 



Twelve specimens were taken oft' Cliama and Spondylus at Mazat- 

 lan, Mexico. The most perfect specimen in the lot is on tablet 

 1965, Liverpool collection, British Museum. It has six post-nuclear 

 whorls and measures: Length 2.5 mm., diameter 0.85 mm. 



ODOSTOMIA (MIRALDA) EXARATA Carpenter. 

 Plate 19, fig. 2. 

 Parthenia exarata Carpenter, Cat. Mazatlan Shells, 1856, pp. 415, 416. 



Shell elongate-ovate, white. Nuclear whorls obhquely immersed, 

 only the tilted edge of the last volution is visible. Post-nuclear 

 whorls marked by two very strongly elevated spiral keels wliich 

 divide the space between the sutures into three equal parts. The 

 posterior of these keels shows weak crenulation. Periphery of the 

 last whorl marked by a tliird keel wliich is almost as strong as those 

 on the spire. A fourth keel considerably less strong occupies the 

 middle of the base. The rounded spaces between the keels are 

 marked by feeble lines of growth. Aperture irregularly oval; pos- 

 terior angle obtuse; outer lip angulated by the keels; columella 

 strong, reflected, provided with a weak fold at insertion; parietal wall 

 covered with a thin callus. 



Doctor Carpenter's type and another specimen were taken from 

 Chama at Mazatlan, Mexico. The type is on tablet 1966, Liverpool 

 collection, British Museum. It has five post-nuclear whorls and 

 measures: Length 6.3 mm., diameter 0.8 mm. 



ODOSTOMIA (MIRALDA) TEREBELLUM C. B. Adams. 



Plate 19, fig. 4. 



Cingula (?) terebellum C. B. Adams, Ann. Lye. Nat. Hist, of N. Y., 1852, p. 406. 



Shell elongate, ovate, milk-white. Nuclear whorls completely 



immersed in the first of the succeeding turns, above which the 



tilted edge of the last volution only projects, wdiicli shows faint 



traces of spiral lirations. Post-nuclear whorls ornamented with two 



