164 Mammalogy in the United States in 1879, [March, 
dog or cat, appear to have been established, notwithstanding 
repeated assertions that skunk bite is always and necessarily fatal. 
To the elucidation of fossil mammals the contributions of Mr. 
Marsh and Mr. Cope have been both numerous and important. 
If these still continue, as in former years, to represent the accu- 
mulation of material in the way of new genera and species, and 
the general enlargement of the view, rather than the attainment 
of final results based upon all the data acquired, they neverthe- 
less include important discoveries and generalizations. 
Foremost among these comes Mr. Marsh’s discovery of Jurassic 
mammals in this country. The original announcement was made 
by Mr. Marsh in June, 1878, in the American Fournal of Science, 
with description of Dryolestes priscus from the Atlantosauris beds 
of the Upper Jurassic, the associated fossils being mainly Dino- 
saurians. 
To this succeeded, in July, 1879, the notice of Sty/acodon gra- 
cilis, and in September, 1879, additional remains of Jurassic mam- 
mals were described as Dryolestes vorax and Tinodon bellus. It is 
interesting to observe, first, that the Jurassic genera indicate as 
many new families, and further, that they confirm Mr. Marsh’s — 
original determination of the Atlantosaurus beds as Upper 
Jurassic. 
The same journal for June has also an interesting paper by the 
same on polydactyle horses, recent and extinct. It is illustrated 
with a plate of the genealogy of the horse, showing the modifica- 
tion of the limbs and teeth from Orohippus to Equus. This paper 
defines clearly, for the first time it is believed, the true difference 
between the orders none too aptly named Perissodactyla and 
Artiodactyla by Owen. The difference between the “ odd-toed ” 
and “even-toed” structure is stated to be “a profound one, 
extending to nearly every part of the skeleton, and marking two 
distinct groups of Ungulates. The number of toes has really 
nothing to do with the true distinction, and hence the terms in 
use are especially misleading. The real difference, so far as the 
feet are concerned, is, that in the Perissodactyle type the axis of 
the limb passes through the middle of the third digit (Mesaxonia), 
while in Artiodactyles * 2 outside of this digit (Paraxona), 
between it and the fourt 
Mr. Cope’s Spaho to the same branch of the subject 
during 1879, will all be found in the publications of the Philadel- 
