1883.] ^09 [Cope. 



extent, as it has been protected by basaltic outflows or not. "When so pro- 

 tected, the river flows through comparatively narrow canyons. Where 

 the outflow is wanting, the valley of the river is wider, and the Loup 

 ForK formation remains as wide grassy mesas which extend to the feet of 

 the mountain ranges. 



The age of these beds would have remained problematical but for the 

 fortunate discovery by Mr. Robert Seip, of the skull of a species of Rhi- 

 noceros of the typical Loup Fork genus, Aphelops. It is apparently the 

 A. fossif/er Cope, a species abundant in the Loup Fork beds of Kansas 

 and Nebraska. It was found near the mouth of Dry creek in a conglom- 

 erate bed of the formation. 



In the valley of the San Francisco the Loup Fork beds reach a thick- 

 ness of 500 feet, and consist of sand, clayey sand, soft sandstone, and 

 conglomerates of larger and smaller pebbles of eruptive material, having 

 a near resemblance to those of the region of Santa Fe. 



Second Addition to the Knowledge of the Puerco Epoch. By E. D. Cope* 

 {Bead before the American Philosophical Society, December 7, 1SS3. ) 



Recent collections from the formation above-named, include many finer 

 specimens than have been previously obtained. Skulls of several species 

 in calcareous concretions were received, so that their characters can be de- 

 veloped more fully than heretofore. I mention especially Deltatherium 

 fundaminis ; Periptychus rhabdodon and P. coarctatus ; Haploconus linea- 

 tus ; H. entoconus ; Anisonchus seciorius ; Protogonia plicifera ; Mioclamus 

 turgidus, M. ferox, M. subtrigonus and M. cuspidatus, sp. nov. Some species 

 hitherto rarely seen, prove to be abundant, as Hemithlceus kowalevskianus, 

 Protogonia plicifera, Mioclaenus minimus and M. subtrigonus. With the 

 additional species now described, the number of Mammalia from the de- 

 posit of the Puerco epoch amounts to seventy-four species. 



DlDYMICTIS PRIMUS, Sp. nOV. 



That the genus Didymictis existed during the Puerco epoch, has been 

 already demonstrated by the discovery of the D. haydenianus Cope. This 

 species is of aberrant form however, so that it remained to prove that the 

 typical form had appeared so early in Tertiary time. This is now shown 

 to have been the case by the discovery of the present animal, which is 

 allied to the D. leptomylus of the Wind river and Wasatch epochs. 



The Didymictis primus is known from two maxillary bones with teeth, 



*The "First addition" appeared in the Proceedings of the American Philo- 

 sophical Society for 1883, beginning at page 545. Since that date I have described 

 in the Proceedings of the Philadelphia Academy, 1883, p. 168, the following spe- 

 cies : Periptychus co'irclatus, Pantolambda cavirictu?, Zelodon gracilis (g. n.) and 

 Conoryctes dilrigonus. 



