10 University of Washington Publications in Geology [Vol. I 



areal differentiation of the radiating ribs. The anterior, dorsal margin does not 

 slope obliquely as it does in B. morsel. 



Named in honor of Professor Henry Landes of the Geology Department, 

 University of Washington. 



Dimensions. Length 19 mm. ; height 6 mm. ; width 4 mm. 



Occurrence. At locality 329 (University of Washington Palaeontological 

 Collection) at the bend in the Cowlitz River, near Vader, Lewis County, Section 

 28, Township 11 North, Range 2 West. 



GENUS GLYCYMERIS DA COSTA 



GLYCYMERIS SAGITTATA (Gabb) VAR. DiCK^RSONi n. var. 

 Plate VIII, Figure 5 



Description. Shell of medium size and subquadrate in outline ; dorsal mar- 

 gin slightly convex ; anterior margin nearly straight and sloping downward at an 

 angle of 15 with the dorsal margin and gradually passing into the regularly 

 rounded, ventral margin ; posterior margin broadly rounded, the posterior ventral 

 margin regularly bowed; surface ornamented with numerous close-set, flat- 

 topped radiating ribs, which on the majority of the specimens examined are only 

 well developed on the middle portion of the shell. The anterior and posterior 

 surfaces of the adult specimens show a lack of, or at least poorly developed, 

 radial sculpture, but the lines of growth are more strongly developed. In the 

 young and more immature specimens, the radial ribs are better developed on the 

 anterior and posterior areas, the outline is less quadrate, and the anterior and 

 posterior margins slope downward making nearly equal angles with the dorsal 

 margin, the posterior being a little more convex than the anterior. 



The radiating and concentric sculpture in this variety seems to be less well 

 developed, as exhibited on unweathered specimens, than in Glycymeris sagittata 

 (Gabb). The diverging lines described for G. sagittata have not been noticed 

 even on the worn specimens of this variety. The anterior margin is less rounded 

 than in G. sagittata. The general outline of the shell is somewhat similar to 

 G. hannibali Dickerson, but the width of the interspace in G. hannibali is equal 

 to those of the radiating ribs, while in G. sagittata var. dickersoni the ribs are very 

 much wider in comparison. 



This variety is very abundant, occurring in a narrow, very fossiliferous 

 sandy layer. 



Dimensions. (Average). Length 15 mm. ; height 14 mm. ; width 10 mm. 



