340 5. W. WILLISTON 



conformable with, and undifferentiated from, the red beds below, 

 seems to render any other disposition of the horizon out of the question. 



The differences of theseTossils from those obtained in the Lander 

 region from an horizon fully two hundred and fifty feet below the 

 top of the beds, are such that their contemporaneity of deposition is 

 very improbable. These differences are especially noticeable, inter 

 alia, in the apparent absence of the teeth so characteristic of those 

 and many other American Triassic deposits — teeth usually referred 

 to a somewhat problematical genus of dinosaurs, called Paleoctonus. 

 These teeth, however, are of several types, and it is very probable 

 that none of them belong with dinosaurs. Indeed, the association 

 of one of the forms with the genus Dolichobrachium Williston seems 

 now assured. This genus, however, seems closely allied to, possibly 

 identical with, the genus Theriodesmus from the Karoo beds of South 

 Africa — a problematical genus whose relationships are yet quite 

 unknown. So different, indeed, is the genus, or at least Dolicho- 

 brachium, that it must be ascribed to a distinct group, perhaps order 

 of reptiles. It is interesting, also, to observe that a recent letter 

 from Dr. Broom confirms the reference of the Anomodont-like reptiles 

 described by me to the true dicynodonts. 



Nothing of the kind has been discovered in the Connecticut 

 valley Trias, while the occurrence of true dinosaurs in those beds, 

 as also pseudosuchian crocodiles, none of which have been certainly 

 found in the Triassic deposits of the West, save the Hallopus beds, 

 would indicate that the most eastern deposits are of a different, 

 perhaps later, age. I am much inclined to believe that the Popo 

 Agie beds, which may be contemporaneous with those yielding ver- 

 tebrate fossils in Utah, Arizona, .New Mexico, and Texas, are of 

 early Keuper age, while the Connecticut valley, the Red Mountain, 

 and Hallopus beds of southern Colorado are later in time. 



Taking all the facts into consideration, I believe that the hori- 

 zon of the Red Mountain beds is nearly or quite identical with that 

 of the Hallopus beds of Canon City. 



That the Hallopus beds of Colorado are of Lower Jurassic age 

 there is not a particle of evidence, unless it be in the ornithopodous 

 character of the dinosaur Nanosaurus, a type never before found so 

 low, though confidently expected from the Trias. The primitive 



