446 



University of California Publications in Geology [Vol. 8 



DESCRIPTION OF SPECIES 

 Pelecypoda 



YOLDIA CABNABOSENSIS, n. sp. 

 Plate 48, figure 6 



Shell medium in size, beaks low and inconspicuous, situated about 

 two-thirds the distance from the anterior to the posterior end. An- 

 terior dorsal edge long and very gently convex ; posterior dorsal edge 

 gently concave. Posterior extremity subtruncate to bluntly rounded, 

 the blunt subtruncate end being subangulate at the junction with the 

 posterior dorsal edge and indistinctly separated from the ventral edge. 

 Surface sculptured by somewhat irregular incremental lines or con- 

 centric ribs. On the surface near the posterior end there is a distinct 

 sulcus which reaches from the beak to a little below the angulation on 

 the posterior end. Hinge plate unknown. 



Y. carnarosensis, n. sp., somewhat resembles Y. cooperi Gabb, a 

 recent West Coast species. It differs in the following respects : the 

 posterior end is not so attenuated, the concentric ribbing is not so 

 regular, the distinct sulcus on the posterior extremity is lacking on 

 Y. cooperi. 



Dimensions. — Length about 40 mm. ; height 20 mm. 

 Occurrence. — From San Pablo Group, Carnaros Creek, Napa 

 County. 



PINNA ALAMEDENSIS Yates 

 Plate 48, figure 3 



Pinna alamedensis Yates. Bept. State Mineral, of Calif., 1887, p. 259. 



Pinna alamedensis Yates. Calif. State Mining Bureau, Bull, no. 4, 1894, 

 p. 56, pi. IV, fig. 53. 

 This species has nine concentric inequidistant rounded wrinkles emanating 

 from the open side, and turning toward the hinge at nearly right angles, the 

 entire shell marked by longitudinal narrow ribs (about forty), which, radiating 

 from apex, extend to the basal margin, becoming more indistinct as they ap- 

 proach the lower margin. These ribs, at their intersection with the lines of 

 growth, are ornamented by slight elevations, forming zigzag markings along 

 the lines of growth. The hinge side is straight the entire length, the opposite 

 side running parallel for about one-half the distance from base to apex, where 

 it makes a sharp curve, thence at an angle of about forty-five degrees to the 

 apex. Length 9, width 5, and thickness about 2 inches. Locality, Alameda 

 Creek, Alameda County. Only one specimen found, and that a very fine one, 

 in the center of a round sandstone bowlder. Miocene. 



