24 University of Washington Publications in Geology [Vol. I 



This species is like S. jxirattelus Gabb in size and in the parallel character of 

 the dorsal and ventral margins but differs in the presence on S. clarki of the* deep 

 anterior furrow. 



Named in honor of Professor Bruce L. Clark of the University of California. 



Dimensions. Length 52 mm.; height 17 mm.; thickness 12 mm. 



Occurrence. At locality 342 (University of Washington Palaeontological 

 Collection) on Coal Creek about one-fourth of a mile above Inman-Polson shops, 

 Cowlitz County, Section 2, Township 8 North, Range 3 West. 



COI,UMBIANUS n. Sp. 



Plate X, Figure 3 



Description. Shell large and broad ; dorsal region slightly convex ; anterior 

 end sloping from the dorsal line at an angle of 25 turning more vertically at the 

 middle portion of the shell and passing below into the ventral margin at an angle 

 of 40 ; dorsal line nearly straight ; a deep, anterior sulcus extends obliquely from 

 the beaks to the ventral margin parallel with the anterior margin ; surface smooth 

 except for the growth lines which are moderately conspicuous. 



This species differs from S. clarki n. sp. in being less convex, higher and in 

 the oblique direction of the anterior sulcus. 



Dimensions. Length 45 mm : ; height 21 mm. ; thickness 4 mm. 



Occurrence. At locality 337 (University of Washington Palaeontological 

 Collection) about one-half mile above old dam, on west bank of Coal Creek, 

 Cowlitz County, Section 11, Township 8 North, Range 3 West. 



GENUS CORBULA BRUGUIERE 



CORBUT.A DICKERSONI n. Sp. 



Plate IX, Figures 9, 10 



Corbula hornii Dickerson, 1915, Proc. Cal. Acad. Sci., Fourth Series, Vol. V, 

 No. 3, pi. 4, figs. 5 a, b; not Corbula hornii Gabb, 1864. 



Description.- Shell small, sub-trigonal in outline ; thick ; inequilateral, beaks 

 situated nearer the anterior end ; beaks low and inconspicuous ; anterior dorsal 

 end sloping from the beaks at an angle of 25 rounding into the ventral margin; 

 ventral margin slightly rounded, ending abruptly in the truncated, posterior ven- 



