88 University of Washington Publications in Geology [Vol. 1 



produced. From the beak a ridge extends to the junction of the posterior and 

 ventral margins. Just above the ridge there is a flat to slightly concave surface. 

 Both right and left valves possess concentric sculpture; lunule and escutcheon 

 elongate and fairly distinct. Radial ribs are absent. 



Dimensions Altitude 8 mm.; longitude 12 mm.; thickness 3 mm. 



Occurrence At locality 256 (University of Washington Palaeontological Col- 

 lection) in railway cuts on the O.-W. R. R. & N. Co. one fourth mile northwest of 

 Lincoln Creek Station in Section 27, Township 15 North, Range 3 West. 



Horizon Lowermost Oligocene; Molopophorous lincolnensis Zone. 



GENUS CRASSATELLITES KRUGER 



CRASSATELLITES LINCOLNENSIS n. sp. 



Plate III, Figures 31, 32 and 33 



Description Shell heavy, small, sub-quadrate in outline and equivalve; 

 beaks situated at a distance about one-fourth the length of the shell from the 

 anterior end, moderately high, incurved and directed forwards; anterior dorsal 

 margin evry slightly concave; anterior end sharply but evenly rounded; posterior 

 dorsal margin straight and sloping downwards at an agle of 10; posterior end 

 sharply truncate and making an angle with the posterior dorsal slope of 120 ; 

 basal margin broadly arcuate; a sharp ridge extends from beak to junction of 

 base and posterior margin. Surface sculptured by fifteen extremely well developed 

 concentric ribs upon which and between which there are fine concentric lines of 

 growth. Pallial line simple and situated some distance from the margin of shell. 

 Muscle scars strong and equally developed; hinge plate moderately developed. 



Dimensions Altitude 11 mm.; longitude 13 mm.; thickness 5 mm. 



Occurrence At locality 256 (University of Washington Palaeontological Col- 

 lection) in railway cuts on the O.-W. R. R. & N. Co. one fourth mile northwest of 

 Lincoln Creek Station in Section 27, Township 15 North, Range 3 West. 



Horizon Lowermost Oligocene; Molopophorous lincolnensis Zone. 



CRASSATELLITES MERRIAMI n. sp. 

 Plate I, Figures 7 and 8 



Description Shell small, moderately thick and sub-triangular; beaks low, 

 wide, strongly incurved anteriorly and situated at a distance two-fifths the length 

 of the shell from the anterior end; anterior end sharply arcurate; posterior dorsal 

 margin nearly straight and sloping downwards at an angle of 20 to the posterior 

 end; posterior end sharply arcuate. There is a ridge extending from the beak 

 to the posterior angle and immediately anterior to this there is a slight depression 



