1913] DicJcerson: Fauna of Eocene at Marysville Buttes 



289 



BITTITJM LONGISSIMUM Cooper 



Bittium longissimum. — Cooper, J. G., Catalogue of California Fossils, 

 Bull. 4, California State Mining Bureau, p. 43. 1894. 



''Exceedingly long compared to its diameter; first three or four 

 whorls regularly convex, smooth; the remaining thirteen with ten to 

 fourteen vertical riblets crossed by three revolving ones, which cancellate 

 the surface uniformly; the anterior riblet largest, thus giving the whorl 

 a turreted form; mouth quadrilateral, simple (the basal surface cannot 

 be seen). Length, 0.55 inch; breadth, 0.0(3; mouth, 0.03. The shell had 

 at least sixteen whorls, and the smoothness of the upper ones may be 

 due to erosion. It much resembles the living B. asperum Gabb (stouter 

 with thirteen whorls), a variety of which is also turreted. (See Pal. 

 of California, 11, p. 12, pi. 2, f. 20}. Marysville Buttes, only found by 

 Mr. Watts." 



CARDIUM DALLI, n.sp. 

 . Plate 14, figures 4a, 4t>, and 4c 



Shell, thin, broad, cordate, equilateral, beaks central, prom- 

 inent, approximate ; hinge-line, nearly straight. Anterior and 

 basal margins form a regular curve; the posterior margin is 

 straight. The surface is marked by minute rounded, radiating 

 ribs excepting on the posterior face of the shell which is covered 

 by about 25 larger ribs rounded on their posterior sides and 

 granulated on their anterior sides. These larger ribs are set off 

 from the finer ribs by a sharp angle which extends from the 

 beak to a point on the basal margin a fifth of the distance from 

 the posterior margin. The posterior face is decidedly concave. 

 The immature forms are frequently bluish on the beaks. The 

 concentric lines of growth are as prominent as the ribs. This 

 uives the shell surface a beautiful reticulated appearance. 



University of California Localities 1853 and 1856. 



Named in honor of Dr. W. II. Dall, Palaeontologist, Smith- 

 sonian Institution. 



This species differs from Cardium cooperi Gabb in having 

 larger granular ribs on the posterior face distinctly set off from 

 the fine)' ribs on rest of the shell. Its ornamentation is entirely 

 different from that of Cardium breweri Gabb but the shape is 

 somewhat similar. The posterior margin is straight in C. dalli, 

 n.sp., while that of C. cooperi is rounded. 



Dimensions: Height, 18mm; length 17mm. 



