152 BULLETIN 68, UNITED STATES NATIONAL MUSEUM. 



ODOSTOMIA (CHRYSALLIDA) OVATA Carpenter. 



Plate 15, figs. 7, la. 

 Chrysallida ovata Carpenter, Cat. Mazatlan Shells, 1856, p. 417. 



Shell ovate, wliite. Nuclear whorls obliquely immersed in the first 

 of the succeeding turns above which only the tilted edge of the last 

 volution projects. Post-nuclear whorls slightly rounded, well con- 

 tracted at the sutures, and moderately shouldered at the summit, 

 marked by nodulose slighth^ retractive axial ribs of which 20 occur 

 upon the first to second, 18 upon the third, and 22 upon the penulti- 

 mate turn. In addition to the ribs the whorls are marked between 

 the sutures b}^ four spiral cords considerably less strong than the ribs, 

 which render them nodulous at their junction. The spaces inclosed 

 by the ribs and spiral cords are deep round pits. Sutures well marked 

 but not channeled. Periphery of the last whorl marked by a narrow 

 spiral groove. Base well rounded, marked by six strong broad 

 rounded almost equal and equally spaced spiral cords, the grooved 

 spaces between which are marked by numerous fine axial threads. 

 Aperture oval, slightly effuse anteriorly; posterior angle acute; outer 

 lip rendered slightly sinuous by the spiral cords; columella slender 

 and curved, provided wdth a fold, deep within, at its insertion; parie- 

 tal wall covered by a thin callus. 



Three specimens of this species taken from Spondylus at Mazatlan, 

 Mexico, are on tablet 1968, Liverpool collection, British Museum. 

 One of these has five whorls and measures: Length 3.9 mm., diameter 

 2.1 mm. 



ODOSTOMIA (CHRYSALLIDA) CINCTA Carpenter. 

 Plate 15, figs. 2, 2a. 

 Chrysallida cincta Carpenter, Rep't Brit. Assn. Adv. Sci., 1864, p. 659. 



Shell elongate-ovate, vitreous. Nuclear whorls smooth, deeply 

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

 tilted edge of the last volution projects. Post-nuclear whorls well 

 rounded, marked by vertical axial ribs which are strongest near the 

 summit, becoming much enfeebled as they pass to the suture. Of 

 these ribs 18 occur upon the second and third and 20 upon the fourth 

 whorl. In addition to the ribs the whorls are marked by four broad, 

 strong, spiral keels which form nodules at their junction with the ribs. 

 On the last whorl the axial sculpture is obsolete on the anterior half 

 between the sutures. Sutures subchanneled. Periphery of the last 

 whorl marked by a strong keel. Base well rounded posteriorly, effuse 

 anteriorly, marked by six low, spiral cords, the two nearest the um- 

 bilical area being very faint. Aperture oval, decidedly effuse ante- 

 riorly; posterior angle acute; outer lip rendered sinuous by the spiral 

 cords, thin, showing the external sculpture within; columella slender, 

 very long, almost straight, reflected, reenforced by the base, provided 

 with a weak fold at its insertion. 



