1916] Weaver: Tertiary Faunal Horizons 39 



also extending from the beak. Surface of shell ornamented with concentric lines 

 of growth and minor ribs which are not very strong but are evenly distributed 

 over the surface of both valves. Dorsal inner margin of shell crenulate; muscle 

 scars well developed; palial line simple; posterior lateral tooth large and anterior 

 cardinal well developed. 



Dimensions Altitude 19 mm.; longitude 30 mm.; thickness 10 mm. 



Occurrence At locality 241 (University of Washington Palaeontological Col- 

 lection) on Stillwater Creek about one half mile above junction of Olequah and 

 Stillwater creeks and one fourth mile below crossing of county road in Section 25, 

 Township 11 North, Range 3 West. 



Note This species bears a close resemblance to Crassatellites cowlitzensis 

 Weaver. It is, however,, more attenuated posteriorly, thinner, higher and external 

 sculpture less well developed. 



Horizon Tejon formation; upper Eocene. 



CRASSATELLITES DALLI n. sp. 

 Plate II, Figures 15, 16, 17 and 18 



Description Shell large, thick, robust, roughly triangular, moderately convex 

 and very noticeably attenuated at the posterior end; beaks prominent, high, broad, 

 anteriorly incurved and situated a little less than one-third the distance of the 

 length of the shell from the anterior end. Anterior dorsal margin slightly con- 

 cave and sloping downwards from the beaks at an angle of 40; anterior margin 

 evenly and sharply arcuate; basal margin broadly arcuate; posterior dorsal margin 

 noticeably concave and sloping downwards from the beaks at an angle of about 

 55 for a short distance and then broadly curved to the posterior end where it is 

 obliquely truncated. A noticeable ridge extends from the beaks to the posterior 

 end and immediately anterior to this there is a broad but fairly well defined groove. 

 Surface of valves ornamented by well developed concentric lines of growth equally 

 developed from beak to basal margin. Radiating ribs are absent. Inner margins 

 of valves are finely but evenly crenulated. Lunule narrow, cordate and very deeply 

 impressed and the concentric lines of growth on the valves continue across the 

 surface of the lunule; escutcheon large, broad and deeply sunken especially near 

 the beaks. Hinge plate very heavy and broad; posterior lateral teeth well devel- 

 oped ; anterior right cardinal sharp and pointed ; muscular scars deep and large ; 

 palial line simple. 



Note This species is extremely common in the Tejon Eocene of Lewis and 

 Cowlitz counties. It is most often associated with a fauna chiefly made up of 

 Ostraea idraeensis and Fenericardia planicosta. The specimens are usually ex- 

 cellently preserved so that all portions of the shell may be readily studied. This 

 species is named in honor of Dr. W. H. Dall of the U. S. National Museum, whose 



