1922] Trask: The Briones Formation, of Middle California 151 



Family Veneridae 

 Genus VENUS Linne 

 YENUS BRIONIANA, n. sp. 

 Plate 5, figure 1 

 Type.— No. 12377, Univ. Calif. Mus. Pal. 



Shell large, subcircular in outline, inequilateral, height about equal to width; 

 anterior dorsal edge short, concave; posterior dorsal edge long and very gently 

 convex; ventral margin strongly arcuate; surface of shell ornamented with 

 numerous concentric undulations, on and between which are smaller incremental 

 lines; hinge plate unknown. 



Dimensions. — Type specimen U. C. no. 12377; alt., 88.5 mm.; width, 86. 5 mm. 



Occurrence. — Briones formation, U. C. loc. no. 177. 



This species resembles V. conradiana Anderson, 24 found in the 

 Temblor formation (Monterey group) in the southern part of the state, 

 but it differs from the latter in that it is more symmetrical in shape, 

 less produced posteriorly, and it possesses a fuller anterior ventral 

 margin. 



Genus TIVELA Link 

 TIVELA MEREIAMI, n. sp. 

 Plate 6, figures la and 1ft 

 Type.— No. 12378, Univ. Calif. Mus. Pal. 



Shell medium in size, height almost equal to width, ventricose, line of 

 greatest ventricosity anterior to middle of shell; surface with slight depression 

 posterior to middle; beaks prominent, only slightly prosogyrous, and a little 

 posterior to middle of shell; dorsal margins straight, subacutely depressed, with 

 greatest depression near beaks; posterior dorsal margin longer than anterior and 

 with a slight depression, which is coexistent with the depression posterior to the 

 middle of the shell; ventral margin strongly arcuate anteriorly; surface smooth 

 except for fine incremental lines; hinge jilate heavy; right valve with three 

 cardinals; anterior cardinal nearly obsolete and very close to the dorsal margin; 

 middle and posterior cardinals about equal in size, the posterior being somewhat 

 the longer; nymph plate heavy and longer than any of the cardinals; anterior 

 clasper long, with inner crest considerably below the level of the dorsal margin. 

 The species is quite distinct because of its ventricosity, rounded dorsal margins, 

 and peculiar hinge. 



Dimensions. — Type specimen U. C. no. 12378; alt., 62.3 mm.; width, 66.8 mm. 

 Occurrence. — Briones formation, U. C. loc. no. 3582. Known only by right 

 valve. 



Named in honor of Dr. J. C. Merriam. 



24 Anderson, Proc. Cal. Acad, Sci., ser. 3, vol. 2, p. 195, pi. XIV, 1905. 



