THE NAUTILUS. 15 



is subcircular and very oblique. The peristome is thin, its 

 margin only slightly thickened and scarcely at all expanded or 

 reflexed except at the base. There is an excessively delicate 

 parietal callus. The type measures, alt. 8, major diam. 16.5, 

 lesser diam. 14 mm. ; diam. of umbilicus 2 mm. ; aperture 8 x 

 8 mm. 



Largest specimen, alt. 11, major diam. 19 mm. 



Smallest adult, alt. 7, major diam. 15 mm. 



lype : Cat. No. 3733 of the writer's collection. A paratype 

 is Cat. No. 117086 of the Academy of Natural Sciences of Phil- 

 adelphia, and another is in the collection of George VVillett. 



Type Locality : Roosevelt, Gila County, Arizona ; in rock 

 slides on north slopes, 2200 ft. altitude. 31 specimens exam- 

 ined, taken by Mr. George Willett, December 15, 1914, and 

 November 1916. 



Remarks : Although the shell characters of this modest species 

 offer no very striking peculiarities, I have been unable to iden- 

 tify it with any of the sixty or so described members of the 

 genus. There is apparently no end to the Arizonan Sonorellas. 

 As compared with the other species of which I have seen speci- 

 mens, S. rooseveltiana seems more than usually thin and fragile. 

 The general porportions of the shell, as the spire, aperture, and 

 so on, are quite variable. 



Some of Mr. Willett' s shells have found their way into other 

 collections as S. coloradoensis Stearns, from the figures a quite 

 different species. 



Redlands, California. 



THE DISTINCTIVE CHARACTEES OF LAMPSILIS MINOK AND 

 L. VILLOSA. 



BY T. VAN HYNING. 



In sending out specimens of the Unionidae of Florida from 

 the Florida State Museum, we have stated of Lampsilis villosa 

 B. H. Wright, and Lavipsilis minor Lea, that it was impossible 

 to differentiate with certainty all of the adult specimens; this 



