6 University of Washington Publications in Geology [Vol. I 



DESCRIPTION OF NEW SPECIES 

 PELECYPODA 



GENUS NUCULA LAMARCK 



NUCULA (Acila) STILLWATERENSIS n. sp. 

 Plate VIII, Figure 8 



Description. Shell small, rectangular in outline ; anterior dorsal margin 

 nearly straight, posterior ventral margin nearly straight, sloping to a broadly 

 rounded anterior end which approaches the dorsal margin with greater convexity ; 

 escutcheon impressed but not defined by an incised line ; central portion of the 

 area of the escutcheon raised, protruding slightly beyond the posterior margin; 

 surface ornamented with radiating ribs medium in strength; above the central 

 portion of the shell the divarication is single, below the mid-area the series of 

 divarication is comparatively wide, the duplication increasing ventrad forming 

 five sets along the ventral margin ; the area of divarication occupying the middle 

 third of the ventral portion of the shell ; lunule not defined ; surface with heavy, 

 impressed growth lines forming wide undulations on the surface of the shell. 



Dimensions. Length 11 mm.; height 9 mm.; width 8 mm. 



Occurrence. At locality 319 (University of Washington Palaeontological 

 Collection), McClarety ranch on the south bank of Stillwater Creek, one mile 

 west of Vader, Lewis County, Section 30, Township 11 North, Range 2 West. 



GENUS LEDA SCHUMACHER 



LEDA COWUTZENSIS n. sp. 

 Plate X, Figure 4 



Description. Shell small and thin, sub-oval in outline ; posterior end ros- 

 trate and pointed ; anterior end regularly and broadly rounded, ventral margin 

 curved, posterior end sloping at an angle of 30 to the ventral line terminating 

 at the dorsal margin in a beak; posterior dorsal margin directed downward and 

 concave; lunule narrow and elongate, only slightly impressed and limited by a 

 fine line ; escutcheon narrow and impressed ; surface ornamented with concentric 

 ribbing which continues from the anterior margin, regularly to the rostrum, the 

 ribs are numerous with only slight interspaces, they are prominent and have the 

 appearance of slightly overlapping each other from the ventral region toward the 



