THE MAMMALIA OF THE DEEP RIVER BEDS. 61 



marked horizon. Together, the two series tend to bridge over the gap between the 

 John Day, on the one hand, and the typical Lonp Fork, though they by no means 

 completely close the hiatus. It is a more difficult task to correlate these beds with 

 their European equivalents. The Loup Fork horizon was referred by Leidy and 

 Hayden to the Pliocene, a view which is still maintained by some authorities, but, as 

 Cope has shown, the determination rests upon the supposed occurrence in these beds 

 of forms having a very modern facies, and which were very probably derived from 

 newer overlying strata, since, in typical Loup Fork exposures not covered by these 

 newer beds, the modernized forms have not been found. The recent discovery of the 

 Blanco beds, of Texas, with their true Pliocene fauna (see Cope, No. 11), lends 

 additional force to Cope's contention that the Loup Fork should be referred to the 

 upper Miocene. Branco has objected to this correlation, as follows : 



" Eine scharfe Parallelisirung wird hier durch die verschiedene Zusammensetzung 

 der beiderseitigen Faunen erschwert, Auf der einen Seite fehlen der Loup Fork 

 Gruppe echt miocaene Formen wie Anthracotlierium und Ancliitlierium und es treten 

 dafiir Geschlechter von jugendlicherem Aussehen wie Protoliippus und Hippidium 

 auf. Andererseits aber reprasentiren nicht nur die amerikanischen Oreodontidce 

 ungefahr ein mit dem europaischen Ccenotherium ubereinstimmendes Entwicklungs- 

 stadium, sondern beiden Faunen sind auch direct Steneqfiber, Amphicyon, Tetraloph- 

 odon, Hipparion und Procervulus gemeinsam. Man wird also mit Cope diese Paral- 

 lelisirung der Loup-Fork-Gruppe mit dem Miocaen Europa's im Allgemeinen gelten 

 lassen miissen, wenn gleich man nicht iibersehen darf, dass dieselbe durch Formen wie 

 Protohippus und Hippidium, welche dem Pferde der Jetztzeit bereits recht naheste- 

 hen, sowie durch das Vorkommen von Dicotyles, Hystrix und Mustela einen entschie- 

 den jugendlicheren Charakter erhalt als die miocaene Fauna Europa's" (No. 2, 

 p. 149). 



These objections rest, for the most part, upon the incorrect identifications of 

 European and American genera, which were current at the time Branco's paper was 

 written. As will be seen in the sequel, Ancliitlierium is present in the lower Loup 

 Fork and not in the White Eiver and John Day, the equines of which formations 

 have been erroneously referred to that genus. The absence of Antliracotherium from 

 the Loup Fork is of no weight, since the genus is quite unknown in America. The 

 occurrence of H/strix, Dicotyles and Mustela in the Loup Fork beds is extremely 

 doubtful, the identifications being made on very imperfect specimens. The reference 

 of Hippidium to this horizon is also very doubtful and has not been confirmed. If, 

 as is almost certainly the case, the equine series is of American origin, there is noth- 

 ing surprising in the fact that the series should be, on this continent, one stage in 



