Geological Papers. 207 



marked by twenty-two radiating ribs, which are acute in young 

 shells, becoming rounded as they increase in size, and ultimately 

 becoming distinctly flattened on top; these are crossed by irregular, 

 curved, subsquamose plates, which, toward the beaks, lose their 

 lamular character and are represented by little tubercles; posterior 

 face of shell costate, but the ribs are less prominent; the interior 

 spaces between the ribs are narrow and usually flat, though some 

 are concave." 



Dimensions of largest specimens obtained: Alt., 73; lat.,67; diam. 

 of right valve, 19. 



This is quite a numerous species in the Pliocene at Quillayute, 

 Wash. 



Pliocene: Humboldt county, California (Gabb); Quillayute, 

 Wash. (Reagan). 



Subgenus Cerastoderma Morch, 



Shell rotund or obovate, with strong ribs obsoletely granulore 



or intricate or smooth ; no posterior or anterior area ; channels 



single; hinge normal (Arnold). 



36. Cardium (Cerastoderma) corhis Martyn. Plate IV, fig. 36. 



Cardium corbis Mart., Pectunculus corhis Mart., Univ. Conch., pi. XXVIII, 

 fig. 2, p. 1784. Carpenter, Brit. Assn. Rept., 1863, p. 642; equals C. 

 californicum Con. and C. nuttallii Con. (see Gabb, Pal. Cal., vol. II, p. 

 98, 1869). Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 232. Keep, 

 West Coast Shells, p. 180, fig. 53, 1892. Dall, Trans. Wagner Inst. Sci., 

 vol. Ill, part 5. 1900, p. 1093. Arnold, Mem. Cal. Acad. Sci., vol. Ill, p. 

 140, 1903. 



Shell very variable, large, subtrigonal, ventricose ; umbones 

 prominent, anterior; surface ornamented with about thirty to 

 thirty-seven regular, slightly squarish, close set, radiating ribs, 

 which are occasionally rugose, the ridges being less rounded near 

 the posterior margin ; inter-rib spaces channel-like grooves ; mar- 

 gin crenulated ; interior not seen. 



Dimensions: Alt., 38.5; lat., 35; diam., 24. 



Three specimens of this species were found on the north bank 

 of the Bogachiel river in the Pliocene formation near Mr. Earl 

 Wilson's homestead, some five miles southeast of Quillayute post- 

 office. 



Living: Kamchatka, Santa Barbara to Kodiac ( Cooper). 



Pleistocene : S&n Francisco, San Pedro, Monterey ( Cooper) : 

 Santa Barbara, San Pedro (Arnold). 



Pliocene : North bank of Bogachiel river, near Mr. Earl Wil- 

 son's homestead, Quillayute, Wash. ( Reagan). 



