WEST AMERICAN PYRAMIDELLID MOLLUSKS. 19 



KEY TO THE SUBGENERA OF PYRAMIDELLA. 



Shell with axial ribs Pharddella, p. 25. 



Shell without axial ribs. 



Shell umbilicated f Pyramidella s. s., p. 19. 



Shell not umbilicated. 



Peripheral sulcus present Longchi.us, p. 21 . 



Peripheral sulcus absent Voluspa, p. 19. 



Subgenus PYRAMIDELLA Lamarck, s. s. 



Pyramidella Lamarck, Prod, d'un Nouv. Class, des Coq., 1799, p. 76. = Obeliscus 

 ANONYMOUS, Museum Calonnianum, 1797, p. 24. ^= Pyramidellus Montport, 

 Conch. Syst., vol. 2, 1810, p. 499. 



Shell of many whorls, tiirrited, umbilicated; columella with three 

 folds; outer lip usually reenforced within, at irregular intervals, by 

 spiral lamellar thickenings. The sculpture consists of mere lines of 

 growth and very fine spiral striations. 



Type. — Trochus dolahratus Linnaeus. 



PYRAMIDELLA (PYRAMIDELLA) BAIRDI, new species. 



Plate 1, figs. 5, 5a. 



Shell broadly conic, milk-white, with a narrow pale yellow band 

 at the periphery, deeply, broadly umbilicated. Nuclear wdiorls at 

 least two and one-half, forming a depressed helicoid spire, whose axis 

 is at right angles to that of the succeeding turns, in the first of which 

 it is about one-half immersed. Post-nuclear whorls well rounded, 

 faintly roundly shouldered at the summit. Sutures well impressed. 

 Periphery and base of the last whorl somewhat inflated, well rounded. 

 Entire surface of spire and base marked by exceedingly fine lines of 

 growth, and microscopic closely spaced spiral striations. Aperture 

 rather large; posterior angle acute; outer lip thick w^ithin, where it 

 is reenforced by six short spiral lirations, three of which fall anterior 

 and three posterior to the periphery; columella straight, slender, 

 provided with three folds, the posterior of one of which is strongly 

 lamellar and at some little distance anterior to the insertion; the 

 other two are less strongly developed and much more oblique. 



The type (Cat. no. 73932, U.S.N.M.) has six post-nuclear whorls 

 and measures: Length 5.1 mm., diameter L7 mm. It comes from 

 the Gulf of California. 



Named for W. Baird. 



Subgenus VOLUSPA Dall and Bartsch. 



Voluspa Dall and Bartsch, Proc. Biol. Soc. Wash., vol. 17, 1904, p. 4. 



Shell of many whorls, turrited, smooth, devoid of all sculpture 

 other than mere lines of growth; not umbilicated; columella pro- 

 vided with three folds; outer lip frequently reenforced within at 

 irregular intervals by spiral lamellar thickenings. 



Type. — Pyramidella auricoma Dall. 



