NO. 2 PYRAMIDELLID MOLLUSKS — BARTSCH 53 



The base is hemispherical and smooth. The aperture is broad and 

 obliquely oval ; the columella is slender with an oblique fold a little 

 below its insertion ; the outer lip is thin. 



The two cotypes, U.S.N.M. No. 561661, come from the Pliocene 

 deposits of North St. Petersburg, Fla. The young specimen has the 

 nucleus and 6.1 postnuclear whorls and measures: Length 2.2 mm., 

 diameter 0.7 mm. The other cotype, a fragment, consists of the last 

 4.1 whorls and measures : Length 3.5 mm., diameter i mm. 



The very regular elongate-conic form and different spiral sculpture 

 easily distinguish this species from Pyrgiscus hebeae (p. 52). 



HYBRIDIZATION AMONG MOLLUSKS 



The Pliocene deposits of North St. Petersburg, Fla., have yielded 

 another very variable complex in the family Pyramidellidae. This 

 complex recalls Turbonilla {Pyrgiscus) tcnuicula Gould of the West 

 Coast of America, of which I wrote, in 1909, in the Monograph of 

 West American Pyramidellid Mollusks (U. S. Nat. Mus. Bull. 68, 

 p. 92) : 



Turbonilla (Pyrgiscus) tenuicula Gould is the most abundant and most vari- 

 able species of all the West American forms, presenting many varieties or in- 

 cipient species; to describe these would not aid science or the collector, but 

 would only add to the confusion which this paper is intended to dispel. 



A second very variable complex on the west coast was noted in the 

 same paper and described on pages 160-161 as Odostomia {Chrysal- 

 lida) virgmalis Dall and Bartsch : 



This is the most variable and the most abundant member of the subgenus 

 Chrysallida. On some the axial ribs extend only over the first two cords below 

 the summit, on others they extend strongly over the periphery and part of the 

 base. The spiral cords also vary in number and strength. The general form, 

 however, seems quite constant. 



A similar state of affairs was noted in the northeast Atlantic and 

 described as Turbonilla (Pyrgiscus) winkleyi Bartsch (Pyramidellidae 

 of New England and the Adjacent Region, Proc. Boston Soc. Nat. 

 Hist, vol. 34, No. 4, pp. 90-91, 1909). From this I quote: 



This is probably the most abundant and variable species on the Atlantic coast. 

 The above description shows that the sculpture in a single specimen, the type, 

 is quite variable. The variability is emphasized when we examine such a wealth 

 of material as has been at our disposal. (177 si>ecimens from 2y localities.) The 

 axial ribs may be crowed or distantly spaced, the spiral markings may vary not 

 only in numbers but also in strength, from deep lines of pits, to fine striations. 

 It is one of those forms in which scarcely two individuals present exactly the 

 same phase of ornamentation, resembling in this respect Turbonilla {Pyrgiscus) 



