12 University of Washington Publications in Geology [Vol. I 



Dimensions. Length 37 mm. ; height 33 mm. ; thickness 22 mm. 



Occurrence. At locality 343 (University of Washington Palaeontological 

 Collection) on west bank of Coal Creek about one-half mile above Inman-Polson 

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



GENUS PTERIA SCOPOU 



PTERIA C^ARKI n. sp. 

 Plate X, Figures 5, 12, 15 



Description. Shell small to medium in size ; oblique in outline ; very inequi- 

 lateral, beaks situated one-fifth of the distance from the anterior end; cardinal 

 line straight, anterior end sloping sharply from the cardinal margin at an angle of 

 25 for a short distance then extending vertically to the ventral margin where it 

 swings with a broad curve into the ventral margin; ventral margin broadly 

 rounded and parallel with the dorsal line ; posterior margin well rounded at the 

 ventral end, extending nearly vertical or at a low angle into the dorsal margin ; 

 anterior ear small, posterior ear very broad, subcompressed ; central area of the 

 shell, extending obliquely from the beaks, broad and convex, often marked by an 

 impressed groove which extends between the posterior and anterior slope of the 

 body portion and the basal line of each ear ; surface ornamented with prominent, 

 close, concentric lines of growth; the growth lines curve sharply from the pos- 

 terior dorsal line to the region of the body of the shell, where they turn at 

 almost a right angle and follow the line of the umbonal slope for a short distance 

 then curve regularly and extend parallel with the line of the ventral margin, 

 anteriorly they extend parallel with the slope of the ear ; shell of a light brown 

 coloration, mottled with reddish-brown spots ; the larger and more mature speci- 

 mens have a uniform color of reddish-brown. 



This species is somewhat like Avicula pellucida Gabb but the beak in P. 

 clarki n. sp. is less prominent, the sculpture is more pronounced, and the curve 

 of the concentric lines on the posterior ear is very much different from that 

 exhibited in A. pellucida. In P. clarki they curve at a greater angle from the 

 dorsal line with a deeper sinuosity in the region where the ear merges into the 

 body of the shell. 



Named in honor of Dr. Bruce L. Clark, professor of Paleontology, Uni- 

 versity of California. 



Dimensions. Maximum height 37 mm. ; width 31 mm. ; thickness 14 mm. 



Occurrence. At locality 323 (University of Washington Palaeontological 

 Collection) in bed of small creek entering Olequah Creek, near Vader, Lewis 



