GEOLOGICAL SUEVEY OF THE TERRITORIES. 301 



low that it might almost be described as A -shaped, while the posterior 

 cardinal of this valve is directed very obliquely backward and down- 

 ward, and compressed. The thin lamina dividing longitudinally the pit- 

 between this oblique tooth and the trigonal, emarginate one, is another 

 peculiar feature. 



CRASSATELLINA OBLONGA, (MEEK.) 



A B 



A shows hinge and interior of right valve ; B hinge and interior of left valve ; both 

 2 diam. 



Shell small, short oblong-subtrapezoidal in outline, less than twice 

 as long as high ; valves rather distinctly convex, with flattened sides ; 

 anterior margin rounded ; pallia! margin nearly straight, or sometimes 

 slightly sinuous along the middle ; posterior oblquely truncated above 

 and narrowly rounded below ; dorsal outline sloping rather abruptly in 

 front of the beaks and less distinctly so behind ; beaks moderately 

 prominent, and placed a little in advance of the middle ; posterior 11m- 

 bonal slopes prominently rounded from the beaks to posterior basal ex- 

 tremity ; posterior dorsal region above the umbonal prominences flat- 

 tened ; flanks sometimes a little concave toward the pallial margin. 

 Surface with rather distinct lines of growth. 



Length, 0.73 inch ; height, 0.32 inch ; convexity, 0.30 inch. 



Specifically, this shell is more nearly like the form I have described 

 from the cretaceous near Canon City, under the name Mactra f Cano- 

 nensis, than it is like any other form with which I am acquainted ; 

 though it differs too widely to be confounded with that shell, even where 

 the hinge could not be seen. They both have so much the appearance of 

 the genus Crassatella, externally, that few would hesitate to refer them 

 to that genus where their external characters only could be examined. 



Locality and position: Twelve miles southwest of Salina, Saline 

 County, Kansas; Dakota Group of the Upper Missouri cretaceous 

 series. Collected by Professor B. F. Mudge. 



PACHYMYA ? TRUNCATA. (MEEK.) 



Shell small, longitudinally oblong, very convex ; posterior side long, 

 distinctly and rectangularly truncated, apparently closed ; pallial mar- 

 gin nearly straight, and slightly sinuous along its entire length; 

 anterior margin truncated a little obliquely forward from the beaks to 

 the rather prominent and abruptly-rounded, or subangularly-anterior 

 basal extremity ; cardinal margin nearly straight and parallel to the 

 base ; beaks depressed nearly to the horizon of the dorsal margin, very 

 oblique, somewhat compressed, and placed less than one-fifth the length 

 of the valves behind the anterior extremity ; posterior umbonal slopes 

 quite prominent or subangular, and continued obliquely to the posterior 

 basal angle, so as to divide the surface of each valve into two nearly 

 equal, elongated, inequilateral triangles, the lower of which forms the 

 concave flanks ; anterior muscular scar small, but very deep ; posterior 

 ditto, larger, shallow, suboval; pallial line not distinctly seen, but 



