CRETACEOUS FOSSILS. 183 



Figure, natural size. 



Locality: From a bed of fine clay adjoining the "Peacock," or lower vein of 

 coal, in the Peacock coal-mine, Mount Diablo District, Contra Costa County 

 (Division B.). 



This is the only undoubted fresh-water shell that has thus far been discovered 

 in the California Cretaceous. I detected it in a vein of fine-grained clay, occupy- 

 ing a "fault" in the Peacock or Cumberland vein. All the specimens are more 

 or less distorted, and I was only fortunate enough to get a single comparatively 

 good one. The testaceous substance had apparently lost all of its animal matter, 

 although the ligament of one specimen is still perfectly preserved. The diagnosis 

 of the outline was obtained from the lines of growth on the surface 



MYTILUS, Linn. 



M. PAUPERCULUS, n. s. 

 PI. 25, Fig. 1G5. 



Shell small, thin, oblique ; beaks terminal, acute ; cardinal 

 line slightly arched, uniting in a regular curve with the posterior 

 side, which is broadly subtruncated above and rounded below ; 

 anterior margin nearly straight. Surface broadly convex, flat- 

 tened above and somewhat abrupt on the sides near -the beak ; 

 ornaments none ; a few faint lines of growth visible near the 

 margins towards the beaks. 



Figure, magnified to nearly twice natural size. 

 Locality: Not rare in Division A., west of Martinez. 



M. ascia, n. s. 



PI. 30, Fig. 259. 



Shell long, narrow, oblique, convex; anterior margin nearly 

 straight, abruptly truncated parallel with the border; cardinal 

 margin slightly arched ; anterior and posterior margins parallel, 

 basal truncated somewhat convexly and at right angles to the 

 two adjoining sides, uniting with them by rounded angles. Sur- 

 face marked only by a few indistinct lines of growth. 



Figure, natural size. 



Locality: Found at Fort T6jon ; but rare. 



