TERTIAEY FOSSILS. 19 



Locality: From the Miocene, west of Martinez; collection of Mr. Bemond. 

 The species appears to be rare. I have never seen it except in two small slabs, in 

 which, however, a large number of specimens are closely packed. 



HEMIMACTRA, Swains. 

 Spisula, Gray. 



H. LENTICULAKIS, n. S. 

 PI. 4, Fig. 33. 



Shell large, flattened, thin, inequilateral, irregularly sub- 

 quadrate; beaks eccentric, large, slightly curved forwards and 

 inwards; anterior end broadly concave below the beaks, and 

 convex below; base and posterior end regularly convex; cardinal 

 margin sloping, nearly straight. Hinge teeth slender. Pallial 

 sinus moderately deep, round at the base. Surface marked by 

 irregular lines of growth. 



Figure, natural size of an average sized specimen, with a transverse thickness 

 of about 1.3 inch. One specimen is 3.8 inches long and 4.2 wide. 



Localities and position : From the Miocene, south of Martinez, collected by Dr. 

 Fish ; also, west of Martinez, on the south shore of the Straits of Carquinez, and 

 at Griswold's, near New Idria, Monterey County. 



MULINIA, Gray. 



? M. DENSATA. 



PI. 5, Fig. 35. 

 (M. densata, Conrad, pars; P. E. E. Eeport, vol. vi, p. 71, pi. 3. fig. 12.) 



Shell thin, equivalve, inequilateral; beaks large, nearly cen- 

 tral ; anterior cardinal margin broadly concave, posteriorly slop- 

 ing with a slight convexity; base broadly and regularly convex; 

 anterior and posterior ends slightly truncated. Hinge small; 

 teeth slender. 



Figure, natural size, from a specimen rather smaller than the average. 



