WEST AMERICAN PYRAMIDELLID MOLLUSKS. 33 



TURBONILLA (TURBONILLA) PROLONGATA Carpenter. 



Plate 2, fig. 18. 

 Chemnitzia prolongatn Carpenter, Cat. Mazatlan Shells, 185(1, p. 429. 



Shell small, very slender, bluish- white. Nuclear whorls small, 

 two, formin«i; a moderately elevated, helicoid spire, whose axis is at 

 right angles to tliat of the succeeding tin-ns, in the hrst of which it 

 is one-third immersed. Post-nuclear whorls almost flat, rather high 

 between the sutures, slightly contracted at the suture, and weakly 

 shouldered at the summit, marked by well-rounded, slender, pro- 

 tractive axial ribs, of which 12 occur upon the first to fourth, 14 

 upon the fifth, 16 u{)on the sixth, 20 upon the seventh and eighth, 

 22 upon the ninth and the penultimate turn. Intercostal spaces not 

 quite as wide as the ribs. Sutures well impressed, rendered slightly 

 wavy by tlte axial ribs. Periphery of the last whoil well rounded. 

 Base rather long, well rounded, marked by the continuation of the 

 axial ribs, which extend to the slight umbilical chink. Aperture 

 rather large, oval; somewhat expanded anteriorly; posterior angle 

 obtuse; outer lip thin, showing the external sculptin-e within; col- 

 umella slender, somewhat revolute; parietal wall covered by a faint 

 callus. 



The type is on tablet 1995, Liverpool collection, in the British 

 Museum, and comes fi-om Mazatlan, Mexico, It has eleven post- 

 nuclear whorls and measures: Length 5.37 mm., diameter 1.25 mm. 



Subgenus CHEMNITZIA D'Orbigny. 



Chemnitzia D'Orbigny, Hist. Nat. lies Canaries, 1839, p. 77; -(- Euturhonilla 

 Semper (part), Archiv. Nat. Fr. Meek., 1861, pp. 354-361; no type; + 

 Microheliscus Sandberger, Land u. Siissw. Conch, d. Vorwelt, 1874, 

 p. 690; type, TurboniUa (Microbeliscus) inaspectus Fuch^i. 



Turbonillas without spiral sculptui'e, having prominent axial ribs 

 which fuse or terminate at the periphery. The intercostal spaces are 

 deep and sunken and terminate at or a little above the periphery, 

 extending upward to the summits of the whorls. Base smooth, devoid 

 of all sculptine. Columella straight. All our West American species 

 belonging to this group are small, slender forms of semitranslucent 

 bluish-white to milk-white color. 



Type. — Melania campaneUsc Philippi. 



key to the species of the subgenus chemnitzia. 



Adult shell more than 7 mm. long. 



Whorls well rounded Inniolispu, \). 34. 



Whorls flattened gahhiana, p. 35. 



Adult shell less than 7 mm. long. 

 Summit of the whorls tabulated. 



Whorls strongly contracted at the suture u /ii/nuiu. p. 35. 



Whorls only slightly contracted at the suture . . inxricatu. p. 36. 



