216 BULLETIN UNITED STATES GEOLOGICAL SURVEY. \Yol.Y. 



Associated witli it are Spirifer roc!:ymontaniis Marcou, Spiriferina 

 octopUcata Sowerby, Spirigera subtiUta Hall, Semipronites crenisfria 

 Phillips, Axopliyllimi rudis White and St. John ?, and an undetermined 

 small Gasteropod. They were all collected by Prof. L. C. Wooster, who 

 in a private comjnuuication says: "They were obtained from some peb- 

 bles in a conglomerate resting upon the eroded face of tlie granite, 33 

 miles west and 18 miles nortli of Greeley, Colorado. A portion of the 

 pebbles of this conglomerate was evidently derived from the granite 

 upon which it rests." He found no Carboniferous strata in situ in that 

 region; but it is evident that tlxe "pebbles" whicli contain the fossils 

 here noticed had not been transported to any considerable distance from 

 the place of tlieir original deposition. They all belong to tyi)es whichi 

 are common in Coal-measure strata, and most of them are well-known 

 Coal-measure species. 



CONCHIFEPvA. 



Genus jSTuculana Link. 



Nuculana obesa (sp. nov.). 



Shell subov.ate in marginal outline, except that the dorsum is concave 

 behind the beaks, moderately gibbous in front, but attenuated behind ; 

 basal margin regularly and broadly convex ; front regularly rounded, 

 the curvature of the margin only sliglitly lessening between the front 

 and the beaks; postero-dorsal margin concave; the posterior portion of 

 the shell narrow and the posterior margin subangular or sharply rounded 

 from the postero-dorsal to the postero-basal margin; umboual ridges 

 sharply defined, and placed so high as to form angular lateral borders 

 to the concave dorsum behind the beaks, the borders being more sharply 

 defined near the beaks than posteriorly; beaks well defined, incurved, 

 and pointing backward, their average distance from the front being 

 somewhat more than two-fifths the full length of the shell, but this va- 

 ries with the varying length of the x)Osterior portion. Surface marked 

 by fine, regular, raised concentric stdse, which are obsolete or less con- 

 spicuous on the poster© dorsal space between the umbonal ridges than 

 elsewhere. Cardinal teeth about 12 on each side of the be^ik ; cartilage- 

 pit moderately large ; interior markings unknown. 



Length of the most perfect example in the collection, 30 millimeters ; 

 height from base to beaks, 18 millimeters ; thickness, both valves to- 

 gether, 12 millimeters. Some less j)erfect examples indicate a greater 

 size and a proportionally greater elongation x)osteriorly. 



This species is closely related to the Leda helUstriata of Stevens ; but, 

 besides being a larger and more robust form, it differs conspicuously in 

 its laterally flattened and longitudinally stronglj^" concave x)ostero-dorsal 

 area. There can be no reasonable doubt that this form is genetically 

 related to li. heUistriata Stevens sp. ; but the differences here pointed out 

 are evidently constant, and therefore deserve recognition, and the most 



