271 
PAL.EOSYOPS LEIDY, AND ITS ALLIES. 
Geological Succession and Distribution of Species . — It is hardly necessary in this 
memoir to dwell upon the geology and subdivisions ol the Bridger Eocene, as Prof. 
II. F. Osborn, in his memoir on Loxolopltodon, gwci'A a long descri})tion of the geology 
of the Bridger, and the tannal relations of the mammals found in this formation, 
lie comes to the conclusion that thei’e is abundant evidence to show that the 
Washakie is a later formation than the Bridger proper. He further shows 
that the nature of the rocks in the tAvo subregions is difl'erent, and that the 
Washakie contains none of the higher genera of the Ungulates which are so 
characteristic of the Bridger, for example the genera Loxolophodon, Amynodon, 
Triplopiis, Achcenodon. Professor ScotP, in his paper on the “Eocene Lacus- 
trine Formations of the West,” says that the Washakie is characterized by 
“ a great reduction of the Creodonts, and Lemuroids, in the difl'erent type of the 
Dinocerata, in the presence of Amynodon, and in the fact that very few species are 
common to the two basins. ” Professor Scott,^ in a later paper, lurther supports- 
the above AueAV and goes into a long discussion endeavoring to show that the Bridgei 
and Washakie are separate formations having been deposited successively, the 
Bri<lger having as a \Adiole an older fauna than the Washakie. My own studies 
upon the species of Palceosyops from these two formations, support the above 
views and indicate that the Bridger is characterized ly many species of Palceosyops 
and allied genera Avhich are not known to occur at all in the Washakie basin. I 
think it Avill be interesting to enumerate the difl'erent species that characterize the 
tAVO sulidivisions of the Bridger, as tliey furnish important evidence as to the distinc- 
tiveness of these two formations. We^ have already stated that Palceosyops borealis 
is the only species of this genus that is found in W ind Riv'er Eocene. Both the 
species of Limnohyops are confined to the Bridger. In the genus Palceosyops there 
are three species which are peculiar to the Bridger proper, namely, P. Icevidens, P. 
minor, and P. longirostris. Telmatolherium has only one peculiar species confined 
to the Bridger, namely, T. cultridens. The MLishakic has fcAver peculiar species than 
the Bridger proper, but one of these belongs to the most specialized species of the genus, 
and leads almost directly to Diplacodon. These are P. hyognathus, the type Avith the 
much elongated juAv, and P. vallidens which is really a doubtful species and is 
intermediate between P. paludosus, and Telmatolherium. The species that are 
common to both formations are three in number, namely, P. paludosus, P. megar- 
hinus, and T. validus. MY see from the above enumeration that the less s])ecialized 
member of the group, Limnohyops, is confined to the Bridger proper, whereas 
the most specialized genus of this subfamily occurs in both formations, it is true, 
but the most progressive species ol' the genus, T. hyognathus, has been only 
recorded from the Washakie. The above consideration will give support to the view 
that the WLashakie has as a whole a more highly developed fauna as regards P alce- 
osyops than the Bridger, and should be placed higher in its geological horizon than 
'The Eocene Lacustrine Formations of the AA'est. Proc. Am. Ass. Adv. Sci., 1887, page 277.- 
2The Alammalia of tlie I’inta Formation, p. 464. 
