Fossil Freshwater Mollusks from Oregon 



Nautilus, Vol. 12, p. 121, 1899, Nye Co., Nevada, Esmeralda Co., Nevada, 

 Inyo and Kern Counties, California. Pilsbry, Nautilus, Vol. 29, p. ill, 1916. 

 Compared to neomexicana. 



Nine specimens from University of Oregon locality 212 differ 

 from this desert form only in being slightly larger in size. This 

 does not seem a sufficient difference to warrant specific separation. 

 The shape and number of whorls in the two are the same. The 

 nine specimens do not show an appreciable range in size, all are 

 about the same. One which is figured measures : altitude, 2.2 mm. ; 

 diameter, 1-7 mm. 



The generic position of the western representatives of this group 

 has not been satisfactorily determined. Since most of them have 

 been placed in the genus Paludestrina, it seems best to retain them 

 all there until the question can be thoroughly solved. Amnicola 

 has usually been applied to the short spired forms and Paludestrina 

 to the longer ones, a distinction which appears of rather minor 

 value in this case. 



GENUS: VALVATA MULLER 



VALVATA OREGONENSIS, N. SP. 

 Plate 3, figures 1-18; plate 4, figures 1-4 



Valvata whitei Hannibal, Nautilus, Vol. 23, pp. 104, 107, 1900. (First 

 mentioned species.) 



Valvata calli Hannibal, Nautilus, Vol. 23, pp. 104, 107, 1910. 



Valvata tricarinata (Say), Hannibal, Proc. Mai. Soc. Lond. Vol. 10, p. 

 197, 1912 (in part). 



Shell composed of four whorls, marked with none to three spiral 

 carinae. Spire normally low and umbilicus wide, exposing all the 

 whorls to the apex. There is great variation in the height of the 

 spire and with its increase there is a proportionate decrease in the 

 width of the umbilicus. The apical two whorls are flat and planu- 

 late, smooth and shining, unmarked with carinae even when the 

 remainder of the shell may have three. Sculpture is comparatively 

 uniform in character, being composed of fine growth lines. 



MEASUREMENTS 



Diameter, mm. Altitude, mm. 



8.0 5.0 (Type ecannate) 



7.8 5.3 



6.9 3.7 

 5.3 3.8 



6.5 3.7 



6.1 3.2 

 6.3 4.4 



4.6 4.0 



6.2 5.4-5.2 

 5.2 5.0 

 4.6 2.6 



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