188 PALAEONTOLOGY OF CALIFORNIA. 



species already described without figures, and the consequent difficulty in distin- 

 guishing allied species, I have deferred their description until I can compare them 

 with specimens or good figures of those already named, outside of California. 



PINNA, Linn. 



P. Brewerii, n. s. 



PI. 25, Fig. 175, and 175 a. 



Shell long, slender, section subrhomboidal; sides diverging 

 at an angle of 18° or 20°. Surface marked by rounded radiating 

 ribs, on at least one-balf of each valve ; other half apparently 

 crossed by a few radiating lines and one or two oblique ones. 

 The middle of each valve is elevated and, in the crest of this ridge, 

 marked by a broad groove. 



Figures, natural size. 



Localities: Division A., Curry's, south side of Mount Diablo; Martinez and 

 Siskiyou Mountains. 



A small specimen, one inch long, probably of this species, was found at Cotton- 

 wood Creek, Shasta County ; and a fragment of a much larger one, three inches 

 across, apparently distinct, is in the collection of Mr. Bayerque, from Division 

 B., near Mount Diablo. 



TRIGONIA, Brug. 

 T. Tryoniana, n. s. 



PI. 25, Fig. 176. 



Shell elongate, subquadrate, narrowest behind; beaks ante- 

 rior, not prominent, subterminal; hinge-line straight, obliquely 

 eloping; anterior end rounded, base convex in front, straight 

 and sloping upwards behind, posterior end convexly subtrun- 

 cated. Surface marked by two radiating grooves, one of which 

 passes from the beaks to the posterior basal angle ; the other is 

 above it ; between the first and the anterior ends are arranged 

 oblique series of elongated tubercles. These are all crossed by 



