306 S. W. WILLISTON 
of reptiles, already represented since early Permian times in Europe. 
Both they and the associated labyrinthodonts, which had been wholly 
absent since Carboniferous times, show the most intimate affinities 
with the European types, proving beyond doubt the equivalency 
of the deposits yielding them with the Keuper of Europe. And, also 
associated with them, are true dicynodonts—of this I have no doubt— 
forms intimately allied to those of similar age in the Trias of South 
Africa, the first representatives in America of another great group 
of reptiles, the Synaptosauria. Between the horizons yielding Per- 
mian fossils, whether vertebrate or invertebrate, and that affording 
these Keuper Triassic animals, there are, in both Kansas and the 
Lander region of Wyoming, at least a thousand feet of continuous, 
conformable, uninterrupted, and homogeneous deposits of red sand- 
stones, deposits utterly barren of all animal or plant remains. I have 
asked geologists in vain what such deposits mean. One thing they 
do mean, for the Rocky Mountain region at least—continuous and 
uniform physical conditions. What became of the Permian verte- 
brates during this interval we cannot say, for, as I have said, there is, 
I believe, not the slightest trace of them or their descendants in the 
land fauna. And from the east, as also from the west, we get before 
the close abundant evidence of dinosaurs and aetosaurs; and a peculiar 
type of mammals, from Carolina. 
Again comes a most lamentable gap in our knowledge of land 
vertebrates in America, that of the Lower and Middle Jurassic. With 
the Upper Jurassic marine beds, come in the most specialized of the 
ichthyosaurs and highly specialized plesiosaurs and a single frag- 
mentary specimen of a crocodile, the first from the American continent. 
Both the ichthyosaurs and the plesiosaurs show such high evolution 
that we must admit their recent migration from Europe, where indeed 
a closely related ichthyosaur had anticipated our form and the plesio- 
saurs had long been known. 
With the close of the Jura a rich land fauna appears in the Morri- 
son beds, rich but not varied, composed almost exclusively of dino- 
saurs, dinosaurs big, dinosaurs small, carnivorous, herbivorous, walk- 
ing, running, almost flying dinosaurs, of high and low degree, but 
among them all not a single type that is distinctively American, not 
one that is not, prior to this time or as a contemporary with it, known 
