46 



parallel to the posterior dorsal margiiij and a mach shorter anterior lat- 

 eral close to the beak. Of course, it will be impossible to determine the 

 generic characters of these shells until more satisfactory specimens can 

 be obtained, and it is only provisionally that the species is now referred 

 to tbe genus Cyrena. 



I have had this species under consideration for some years, hoping 

 that better specimens would be found ; but, as a second visit to the 

 locality has failed to bring to light any more satisfactory material, and 

 the geologists of the survey desire to have a name by which they can 

 refer to the shell, I have concluded to describe it doubtfully under the 

 genus Cyrena. The specific name is given in honor of Mr. William H. 

 Holmes, the artist of the survey, who discovered the type-specimens. 



Locality and position. — On Ralston Creek, three to four miles north 

 of Golden City, Col., from beds supposed to hold a position from 400 to 

 500 feet above the beds of coal mined at Golden City. Probably of 

 Tertiary age. I th nk Dr. Pale found the same species farther south, 

 between Golden and Colorado Springs, not far from the latter. ISTo other 

 fossils were found associated with it 



Sph^riola? obliqua, Meek. 



Shell (as determined from an internal cast) obliquely oval-subcordate, 

 very gibbous, the greatest convexity being in the central region of the 

 valves ; posterior side very short, and ronnding somewhat obliquely 

 downward and forward into the base, which forms a transversely-serai- 

 ovate or semi-elliptic curve ; anterior side longer and more or less regu- 

 larly rounded ; hinge very short ; beaks prominent, gibbous, and moder- 

 ately incurved, but not directed very obliquely forward, situated at the 

 anterior end of the hinge, nearly over the middle of the valves ; muscu- 

 lar impressions faintly marked, the posterior being placed close up under 

 the end of the hinge; pallial line obscure, but apparently simple. 

 (Surface-markings and hinge unknown.) 



Length, 1.95 inches; height, 1.94 inches; convexity, 1.57 inches. 



I merely place this species provisionally in the genus Sphwriola, as I 

 have done with two similar Upper Missouri Cretaceous forms ; nothing 

 being yet known in regard to the hinges of these shells beyond the fact 

 that they have no lateral teeth. It is quite as probable, and perhaps 

 even more so, that when their hinge-characters can be determined, these 

 species will all be found to present generic differences from Spliceriola. 



The species here under consideration seems to agree most nearly with 

 the Upper Missouri form that we have called S.f cordata, bat it has less 

 elevated and less pointed beaks, and differs materially in its much more 

 oblique form ; its anterior basal margin being so much more prominent 

 than the posterior as to give a decided backward obliquity to the um- 

 bones, excepting their points, which are turned a little torward. 



Locality and position.— ¥rom the highest Cretaceous beds on Left- 

 hand Creek, half-way between Long Mont and Boulder City, Col. 



Rhynchonella Endlichi, Meek. 



Shell attaining a rather large size, subtrigonal, with breadth nearly 

 or qnite equaling the length, the widest part being in advance of the 

 middle, becoming very convex with age anteriorly; posterior lateral 

 margins straight, or but slightly convex in outline, laterally compressed 

 or flattened, and diverging from the beaks, in adult specimens, usually 

 at about right angles or less ; anterior lateral margins rounding to the 



