152 PALAEONTOLOGY OF CALIFORNIA. 



PHOLADOMYA, Sow. 



P. BltEWERII, 11. S. 

 PI. 22, Fig. 123. 



Shell ovate or subquadrate, compressed; beaks anterior, mode- 

 rate in size; buccal end unknown; anal extremity rounded, sub- 

 truncate ; cardinal border nearly straight behind the beaks, gently 

 sloping ; base very slightly convex. Surface marked by twenty- 

 four or twenty-five fine, linear ribs, which radiate regularly from 

 the beaks, covering all the surface, except a narrow portion pos- 

 teriorly, near the cardinal margin, about as wide as two or three 

 ribs ; besides these, the surface is covered by fine, irregular lines 

 of growth. 



Figure, natural size. 



Locality: A single specimen found by Prof. Brewer, at Pence's Ranch, Butte 

 County (Division A.). 



This species approaches P. subelongata, Meek, from Vancouver Island ; but, 

 besides the difference in form, the marked difference in the number of ribs will at. 

 once serve to distinguish them ; the latter species having but sixteen ribs. 



P. NASUTA, 11. S. 

 PI. 30, Fig. 124. 



Shell oblique, convex ; beaks high, anterior, incurved, nearly 

 touching ; umbones prominent. Buccal end obliquely truncated 

 inwards towards the base, nearly straight; posterior end pro- 

 duced, rounded, gaping ; base and anterior end closed. Surface 

 marked by from twelve to sixteen small, radiating ribs, which 

 cover about two-fifths of the surface, leaving a small portion of 

 the anterior end and the posterior third uncovered ; besides 

 these, the whole surface is covered by prominent, irregular, con- 

 centric ribs. 



Figure, natural size. 



Locality: On the shore of the Straits of Carquines, two miles west of Martinez. 

 Collected by Mr. Mathewson (from Division A.). 



