Prof. K. A. von Zittel—On the Mammalia. 407 
Utah and New Mexico the Older Tertiary fresh-water beds cover 
hundreds of square miles and are quite open to investigation, we 
need not relinquish the hope of future fresh discoveries in Europe. 
The excellent researches of Riitimeyer’ on the Bohnerz fauna of 
Switzerland have moreover shown that during the Hocene period an 
unexpected number of genera of a distinctly American stamp lived in 
Europe. The fissures in the Jurassic Limestones filled with mud 
and terruginous-concretions (Bohnerz), in which these forms were 
‘preserved, cannot be directly compared with ordinary sedimentary 
strata. Their infilling was probably a very slow process; it plainly 
began during the Older Hocene period and continued to its close. 
The Bohnerz fauna of Switzerland has, therefore, no individual 
character; forms of Old-Hocene type are mingled in it with those of 
the Middle and Upper Eocene. The earlier forms are, as a rule, only 
indicated by a few isolated teeth, but they nevertheless serve to show 
that several genera, hitherto held to be indigenous to America, lived 
also in Hurope. And this fact is of great importance, since it proves 
not only the unity of origin of the Older Eocene fauna, but also 
the former connection of two regions of distribution, now sharply 
separated. 
II. Mipptz Eocene. 
The conditions of preservation were still more unfavourable in 
Europe during the Middle Hocene than previously. The neigh- 
bourhood of Paris, the fresh-water deposits of Argenton (Indre), 
Bracklesham (Sussex), Issel (Aude), Buchsweiler (Alsace), and some 
few other scattered localities have yielded the scanty remains of a 
mammalian fauna, amongst which may be named the Perissodactylous 
genera Lophiodon, Palgotapirus, Propaleotherium, Paloplotherium, 
Hyracotherium, Pachynolophus, Pernatherium, the Artiodactyle Dicho- 
_bune and the Creodont genus Proviverra. The teeth and fragmentary 
bones and jaws which have been washed together into the Bohnerz 
fissures of the Swiss Jura at Egerkingen, Gdsgen, Mauremont and 
St. Loup, would have better revealed the composition of the Middle 
Hocene mammalia, if they had not contained a commingling of 
remains from all the other divisions of the Eocene period. A 
comparison with the American area, where the renowned Bridger 
or Dinoceras-beds of Wyoming are filled with beautifully preserved 
mammals, is beset with great difficulty for want of material. Fresh 
finds in Europe may yet yield further forms of an American type, 
since all our Middle Eocene genera possess in the Bridger beds, 
either representative forms or are themselves directly represented 
by slightly different species. The Bridger beds contain the follow- 
ing genera: ” 
MARSUPIALIA. Liohippus. Lambdotherium. 
Didelphys. Pachynolophus. Helaletes. 
(Orohippus.) Hyrachius. 
PERISSODACTYLA. ? Helohippus. Colonoceras. 
. Hyracotherium. Lpihippus. Triplopus. 
1 Die eocane Saugethierwelt von Egerkingen. Abh. Schweiz. palaon. Gesellsch. 
1891, Bd. xviii. 
* The Genera most numerously represented are printed in thick type. 
