1916] Weaver: Tertiary Faunal Horizons 85 



edges. Hinge with 26 anterior and 21 posterior V-shaped teeth. Chondrophore 

 small and subumbonal. Adductor muscle scars small; palial sinus short. 



Dimensions Altitude 8 mm. ; longitude 20 mm. ; thickness 7 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 west and 

 north of Lincoln Creek Station in Section 27, Township 15 North, Range 8 West. 

 In this region the bluffs extend above and below the railway track and for a dis- 

 tance along the track of about one mile. Specimens are exceedingly abundant 

 and in an excellent state of preservation. 



Horizon Lowermost Oligocene which in this report is referred to as the 

 Porter Horizon or Molopophorous lincolnensis Zone. 



LEDA LINCOLNENSIS n. sp. 

 Plate III, Figures 23 and 24 



Description Shell of moderate size and thickness. Beaks more nearly cen- 

 tral than in case of Leda washingtonensis. Shell relatively higher and anterior end 

 more broadly rounded than posterior. Surface of shell sculptured by prominent 

 flat topped concentric ribs with interspaces about one and one-half times as wide. 

 Lunule elongate and lanceolate, fairly deep and of about same width as escutcheon; 

 escutcheon deeply impressed and sculptured. Hinge line with 25 anterior V-shaped 

 teeth; interior of chondrophore slightly grooved; palial sinus short. 



Dimensions Altitude 10 mm.; longitude 20 mm.; thickness 8 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 west and 

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



Horizon Lowermost Oligocene which in this report is referred to as the 

 Porter Horizon or Molopophorous lincolnensis Zone. 



GENUS GLYCIMERS DA COSTA 



GLYCIMERIS CHEHALISENSIS n. sp. 



Plate III, Figures 34 and 35 



Description Shell small, sub-triangular in outline, moderately convex, beaks 

 central and small; anterior dorsal margin almost straight and sloping downward 

 at an angle of 55; posterior dorsal margin moderately convex and sloping at an 

 angle of 40 ; base sharply arcuate. Surface sculptured by 45 well developed, 

 flat topped squarish radiating ribs separated by interspaces about once and one- 

 half as wide as the ribs. Near the anterior and posterior ends of the shell the 



