102 PALAEONTOLOGY OF CALIFORNIA. 



I have not been able to expose sufficient of the inner lip to ascertain satisfac- 

 torily whether there arc the requisite folds to place this shell in the genus Faseio- 

 laria. Until more material shall have been obtained, the determination will 

 therefore have to remain doubtful. The species is named from its resemblance to 

 the fresh-water genus Io. 



VOLUTILITHES, Swainson. 



V. Navarroensis, Slmm. ? 



PL 19, Fig. 5G. 



Large, fusiform, thin, tapering nearly equally from the middle 

 towards both extremities. Spire conical ; whorls six to seven ; 

 those of the spire sometimes flattened, sometimes convex below, 

 and flattened or slightly concave near the suture; body whorl 

 flattened near the suture, gently swelling in the middle, and 

 tapering or broadly and regularly concave below. Mouth long, 

 narrow, acute behind, and with the sides nearly parallel in ad- 

 vance ; outer lip acute ; columella with three thin, linear, oblique 

 folds on the middle. Suture distinct, impressed. Surface marked 

 by longitudinal ribs, faintly sinuous, sometimes distinct and 

 prominent, at others nearly obsolete ; commencing a short dis- 

 tance below the suture, and losing themselves about or just below 

 the middle of the whorl. When they are well marked, there are 

 about fourteen or fifteen on the body whorl ; but, as they become 

 less distinct, they are more numerous. These are crossed by six- 

 teen or seventeen revolving ribs ; the first three (sometimes four) 

 of which are small, plain, and placed above the origin of the 

 longitudinal ribs ; the next five or six are represented by a tu- 

 bercle on each longitudinal rib, but are obsolete in the inter- 

 spaces, the rest being plain, or more or less nodose. Three' of 

 the tubercular ribs are visible on the upper whorls. 



Figure, natural size of the largest specimen. 



Locality: Tuscan Springs, abundant; collected by Dr. Veatch. Also found at 

 Pence's Pianch, above Oroville, Butte County; Jacksonville, Oregon; Siskiyou 

 Mountains; Chico Creek, Butte County; and Cow Creek, Shasta County (in 

 Division A.). 



