126 GEOLOGY. 
In Europe it is a Lower Carboniferous and Devonian fossil. In this country it extends from 
the Devonian up through all the Carboniferous strata, and is found in Kansas in what Prof. 
Swallow calls ‘‘Lower Permian rocks,’’ but which this fossil, with the many others we have 
cited as associated with it, indicate should rather be regarded as Upper Carboniferous. 
Large and strongly marked specimens of S. wmbraculum were found by the writer in the 
cherty limestone, the highest member of the series, in the cafion of Cascade river, near the 
junction of the Colorado Chiquito (Flax river) with the Colorado. This rock is continuous 
with that forming the high mesa about the San Francisco mountain, extending to the crossing 
of the Little Colorado, where its upper portion is regarded as Permian by Mr. Marcou. 
At Agua Azul, east of Fort Defiance, at Santa Fé, at Ojo Vernal, and again on Cottonwood 
creek, Kansas, this limestone is exposed; at each place containing this fossil, associated with 
Upper Carboniferous species. 
Mr. Marcou, in The Geology of North America, p. 45, describing his Productus Delawari, 
pronounces the Orthis umbraculum figured by Hall (Stansbury’s Report) as not an Orthis, but a 
Productus and P. Delawari. In this he is evidently in error, as the original specimens, which 
he never saw, are clearly Orthis, as the genus was then limited, and undistinguishable from 
O. umbraculum. 
STREPTORHYNCUS PYRAMIDALIS, (n. sp.) 
Plate II, figs. 11-13. 
Shell nearly orbicular in outline ; elevated, sub-globose; cardinal border somewhat rounded; 
ventral valve high, rising to a cee greater than half the antero-posterior diameter ; beak 
prominent, often much produced and laterally distorted; sometimes nearly equidistant from 
the cardinal and anterior borders, when this valve has a pyramidal form; foramen forming a 
triangle of which the base is usually about one-third the altitude; dorsal valve gently arched, 
highest toward the cardinal edge ; surface marked with about twelve strong radiating costa, 
which are finely but sharply striated longitudinally. This shell is distinguishable from S. occi- 
dentalis, which it somewhat resembles in the character of its surface markings, by its stronger 
cost, more strongly arched valves, broader area, and narrower foramen. 
ity and formation.—Carboniferous limestone over red cross-stratified sandstone at Camp 
70, on high mesa west of Little Colorado. 
STREPTORHYNCUS OCCIDENTALIS, (n. sp.) 
Plate I, figs. 5, 5a. 
Shell depressed, broadly rounded; cardinal border nearly equal to greatest diameter ; ventral 
valve flattened and slightly concave toward the anterior margin; beak produced and generally 
twisted laterally. Cardinal area twice as broad as high; cardinal notch forming a triangle of 
which the base is half the height; dorsal valve slightly arched throughout; surface bearing 
11 to 13 strong radiating coste, which are striated near the anterior margin 
_ This shell is nearly twice the horizontal diameter of S. pyramidalis ; being broader, flatter, 
and less strongly ribbed and striated than that species. With any other described it is scarcely 
likely to be confounded. 
Locality and formation.—Cherty limestone, top of Carboniferous series, Camp 73, in cafion 
of Cascade river. 
ATHYRIS. 
pathy cate subtilita Hall. Stansbury’s Report, p. 409, t. 4, figs. 1-2. 
ae This fossil occurs in large numbers in the cherty limestone on the banks of the Colorado, 
: between the Little Colorado and Diamond river. It is also common in the limestone at Pecos 
