456 GEOLOGICAL SURVEY OF THE TERRITORIES. 



probably belongs to no recognized family. I have every reason to 

 believe that Inoceranius involutus, Sowerby, is a species of this or a 

 nearly allied genus. It has the singular character of being very thin, 

 on the disk and gradually thickening to the margin, in which it agrees 

 with the American shells, and also in the character of the dorsal mar- 

 gin, which appears to be rolled over. This rolling-over, however, does 

 not exhibit the hinge-character, which has no resemblance whatever to 

 that of Inoceramns, and the ridged surface at the top of the hinge is on the 

 outside of the valve, as represented in Sowerby's figure. Table 583, Fig. 

 2. The typical specimen of one valve of the genus has a broad or thick 

 tooth near the anterior margin, and a thick, rounded ridge forming the 

 rest of the hinge. These singular shells were developed in the Upper 

 Chalk of England and America, and, like the Budistce, came suddenly 

 and disappeared forever with the last deposit of chalk. 



H. CAP AX. — Left valve inflated, subrotund, incurved toward the ven- 

 tral margin ; undulations or concentric ridges profound, distant, extend- 

 ing to the posterior hinge-margin, though becoming almost obsolete 

 very near the margin ; interstices regularly and strongly striated. 

 Length and height equal, five inches. Found by Dr. Leconte near 

 Denver. Lioceramus, Fig. 2, Fremont's expedition represents, I think, 

 this species. 



CHAPTER III. 

 THE EOCENE PERIOD. 



A few species from beds of this period were obtained in Wyoming 

 and Colorado, of which the following are new to science. 



MAMMALIA. » 



EOBASILEUS, Cope. 



EOBASILEUS GALEATUS, Sp. nov. 



Eepresented by the greater portion of a cranium of an individual of 

 the size of the Loxolopliodon cornutus. It possesses a greatly-elevated 

 occipital crest, whose superior border presents a median angle up- 

 ward. A short distance in front of it, and connected by a very stout, 

 lateral ridge, there arises, on each side, a large, erect horn-core. The 

 base is • very massive, subquadrate in section, and flattened in front. 

 Posteriorly, it presents a very shallow groove, which is bounded on the 

 outside by a low ridge. The shaft expands gradually, and is propor- 

 tionally flattened from behind forward. The posterior face is flat ; the 

 anterior gently convex. The extremity is transverse-convex, and pit- 

 ted for cartilaginous or corneous attachment. These horns stand on 

 the parietal bones. The frontals extend to their bases, and send a lami- 

 nar expansion backward to the margins of the lateral and posterior 

 crests, covering the parietal in the fundus of the basin, which the 

 former inclose.* 



* Marsh originally stated that these horn-cores in Uintathermm mirahile stand on the 

 frontal ; but later, that it was doubtful whether the frontal supported horns. 



