308 University of California Publications in Geology [Vol. 10 



ventral margin gently convex to nearly straight. Dimensions : Height, 

 32 mm. ; length, 41 mm. ; thickness, 14 mm. 



This species resembles in a general way Periploma argent aria 

 Sowerby. In Periploma clarki, n. sp., the shell is, however, higher 

 and thicker in proportion to its length, the anterior end is much 

 shorter, the posterior end is biangulate, and the posterior dorsal 

 margin straighter. 



Occurrence. — At localities 2276, 2278, 2279; Santa Margarita. 



Named in honor of Dr. B. L. Clark of the Department of Palaeon- 

 tology at the University of California. 



PINNA BICUNEATA, n. sp. 

 Plate 15, figures la, lb 

 Type in Univ. Calif. Coll. Invert. Palae., no. 11307, from locality 2284, near 

 middle of southern boundary of NE % sec. 10, T. 19 S, E. 15 E, M. D. B. & M., 

 about fifty feet above base of Santa Margarita, ten miles northeast of Coalinga. 



Shell elongate-cuneate ; in cross-section thin, acutely elliptical. 

 Hinge line long, nearly straight; ventral margin slightly concave 

 near beaks ; posterior end evenly rounded. Sculptured by approx- 

 imately ten distinct radiating ridges which appear to be absent on 

 lower one-third of shell. 



Dimensions of type with broken posterior end : Length, 96 mm. ; 

 width, 44 mm. ; thickness, 18 mm. ; umbonal angle, 35 degrees. 



This form may be distinguished from Pinna alameclensis Yates, 

 which also occurs in the same beds, by its smaller size, long, straight 

 hinge-line and ventral margin, less number of radiating ridges, and 

 in being thinner in cross-section. 



Occurrence. — In the Santa Margarita, locality 2284, near Coalinga; 

 in upper San Pablo group, locality 1245, Las Trampas Ridge, Concord 

 quadrangle, Contra Costa County ; near Standard Oil Co. Powell 

 well, eight miles northeast of Bradley, Monterey County, Lower 

 Etchegoin ( ?). 



SEPTIFEB MABGABITANA, n. sp. 

 Plate 19, figure 5 



Type in Univ. Calif. Coll. Invert. Palae., no. 11310, from locality 2276, on hill 

 near SW corner of SE % of NE % sec. 10, T. 19 S, B. 15 E, M. D. B. & M. 



Shell long, cuneate, rather thick ; beaks pointed, terminal ; with 

 well-developed umbonal ridge extending to posterior ventral margin. 

 Anterior dorsal margin slightly concave ; posterior dorsal margin 

 regularly convex ; posterior end evenly rounded ; ventral margin a 

 little concave at middle but becoming convex about one-third of 



