CRETACEOUS FOSSILS. 157 



the beaks, sloping upwards, and sometimes nearly straight pos- 

 teriorly. Surface plain, or marked only by lines of growth. 

 Muscular scars rather faint; pallial sinus deep, narrow. 



Figures, natural size. 



Locality: Abundant in Division A., west of Martinez; also found at Pence's 

 Ranch, Butte County. 



This species sometimes attains a size twice as large as Figure 133 a, but can 

 always be distinguished by its straight or slightly convex cardinal margins. 



T. MONILIFERA, n. S. 

 PI. 22, Fig. 134, and 134 a. 



Shell small, subelliptical, equilateral; beaks central, promi- 

 nent, with the cardinal margins sloping symmetrically on each 

 side, straight, or a little convex; extremities regularly rounded, 

 equal; basal margin broadly convex, most prominent in the 

 middle. Surface marked by fine, regular, concentric ribs, with 

 narrow impressed lines between them, except on the posterior 

 fifth or sixth, where they become faint, and are replaced by a 

 series of rather coarser, moniliform, radiating ribs. Hinge com- 

 posed of one small, simple, and a larger bifid primary tooth, and 

 two prominent lateral teeth. Pallial line very faint. 



Figure 134, natural size; Fig. 134 a, magnified view of the posterior half. 



Locality: From Division A., Texas Flat, Placer County; collection of the 

 California Academy of Natural Sciences, presented by Dr. Trask. 



This shell is of the same size and shape as Nucula perequalis, Con., of the Ala- 

 bama "Ripley Group," but can be distinguished by the peculiar external orna- 

 mentation. 



T. OOIDES, 11. S. 

 PI. 22, Fig. 135, and 135 a. 



Shell large, oval, compressed, a fifth longer than wide; beaks 

 small, anterior, subcentral; cardinal margin sloping regularly 

 and convexly on both sides ; extremities regularly rounded, the 

 anterior broadest ; basal margin convex, most prominent in the 

 centre. Surface marked only by rather distinct, irregular lines 

 of growth. 



