1916] Weaver: Tertiary Faunal Horizons 41 



one short, sharp, high, triangular lateral, tooth with a deep grove above; there 

 are two cardinal teeth, the anterior of which is flattened and makes an angle of 

 25 with the vertical axis of shell; posterior cardinal tooth is triangular in cross 

 section with a long, deep groove behind; posterior lateral long and blade like; 

 palial sinus deep and extending in one-third the length of the shell. 



Dimensions Altitude 18 mm.; longitude 22 mm.; thickness 10 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 PITARA ROMER 

 PlTARIA DALU n. Sp. 



Plate I, Figures 1, 2, 3 and 4 



Description Shell of medium size, inflated and ovate to sub-quadrate; beaks 

 moderately high, incurved and situated a distance from the anterior end of the 

 shell of one-fourth the length of the shell. Anterior dorsal margin short and 

 slightly concave; base evenly arcuate; posterior dorsal margin very slightly 

 rounded, sloping downward from the beaks at an angle of 5 to a point one- fourth 

 the length of the shell from the posterior end; from this point it becomes more 

 sharply rounded and slopes at an angle of 45 to the posterior end which becomes 

 more sharply arcuate and merges into the base. Just below the posterior dorsal 

 margin a very faint groove like depression extends from the beaks to the posterior 

 end. Surface concentrically striated by fairly well developed lines of growth. 

 Lunule large, cordate, deep and described by a well-defined impressed line; pal- 

 ial sinus simple and extending into the shell a distance of one-third the length 

 of the shell. Hinge well developed. Anterior left lateral tooth prominent, short, 

 compressed and very slightly bifid; posterior right cardinal bifid; right anterior 

 lateral groove deeply incised; anterior right cardinal narrow and blade-like; pos- 

 terior right cardinal bifid; anterior left lateral high and very slightly bifid; an- 

 terior left cardinal narrow and sharp; posterior left cardinal broad and rather 

 low; groove between posterior lateral and posterior cardinal deep and broad. 



Dimensions Altitude 43 mm.; longitude 57 mm.; thickness 28 mm. 



Occurrence At locality 256 (University of Washinton 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. 



