306 University of California Publications in Geology [Vol. 10 



approximately a right angle ; flattened on sides of posterior portion 

 of shell from beak to posterior dorsal margin. Anterior dorsal margin 

 short and strongly concave ; anterior ventral margin convex, becom- 

 ing nearly straight near anterior end. Posterior dorsal margin long, 

 nearly straight near middle, with increasing convexity towards ends; 

 posterior ventral margin regularly arcuate. Lunule large, strongly 

 depressed ; escutcheon long, rather narrow. Surface of shell orna- 

 mented on sides by prominent concentric growth lines and radiating 

 ribs of medium width. Middle and posterior cardinal tooth of right 

 valve bifid ; anterior cardinal small ; nymph plates long and heavy. 

 Posterior cardinal heavy, bifid ; anterior cardinal long and rather 

 narrow. Dimensions: Height, 71 mm.; length, 80 mm. 



Chione temblorensis Anderson resembles Chione semiplicata, n. sp. 

 The latter, however, may be readily distinguished by not having the 

 marked depression on the sides at the posterior end and has more 

 anterior beaks. From Chione elsmerensis English it differs in having 

 shorter and more concave anterior dorsal margin, more convex ventral 

 margin and weaker hinge. 



Occurrence. — At localities 2276, 2283, in the Santa Margarita. 



OSTREA TITAN CORRUGATA, n. var. 

 Plate 16, figure 1 ; plate 17, figure 1 

 Type a well preserved specimen of lower valve, no. 11309, in Univ. Calif. Coll. 

 Invert. Palae., from locality 2284, near middle of southern boundary of NE % 

 sec. 10, T. 19 S, R. 15 E, M. D. B. & M., about fifty feet above base of formation. 



Shell large, very heavy, when full grown sub-ovate but in earlier 

 stages of very irregular outline. Surface sculptured by well marked 

 growth lines which at the edges are irregularly folded into prominent 

 radiating ridges. Ligamental groove wide, triangular, extending 

 nearly across anterior end of shell. Muscular impression large, 

 rectangular, almost invisible in type. Dimensions of lower valve : 

 length, 235 mm. ; width, 150 mm. ; height, 120 mm. 



Distinguishable from the typical Ostrea titan Conrad which is 

 also found in the Santa Margarita formation by the prominent folds 

 on surface and the greater convexity of lower valve. 



Occurrence. — At locality 2281, Santa Margarita, about ten miles 

 northeast of Coalinga, Fresno County; northern end of Huasna Val- 

 ley, San Luis Obispo County; Vineyard Creek anticline, Monterey 

 County. 



