522 M. G. MEHL 



Wyoming,^ is known from the humerus, teeth, and coraco-scapula 

 only, there is Httle basis for comparison. The first two elements 

 and especially the coraco-scapula are suggestive of a more massive 

 build than that of the present specimen. There is, however, 

 the possibility that these two forms are identical, an uncertainty 

 that must remain till more abundant material is to be had. In 

 some respects it resembles some of the early dinosaurs. The hollow, 

 slender leg bones, the slightly biconcave vertebrae, are suggestive 

 of the Theropoda and the perforate acetabulum is typically dino- 

 saurian. Unlike the condition in this group of dinosaurs, however, 

 each sacral rib is supported by a single vertebra. While this is a 

 condition found in the sauropod dinosaurs, their solid bones, the 

 expanded neural canal of the sacrum, and many minor points are 

 very different from the form under discussion. In the future it 

 may be shown that the genus Palaeoctonus of Cope is related to 

 the form here described as, indeed, there is a possibility that 

 Palaeoctonus and Dolichobrachium are identical. When the remains 

 of the latter genus were discovered there were present portions of 

 a skull in a powdery condition, too poorly preserved to be saved. 

 According to Dr. Williston there was enough seen of the teeth, 

 however, to suggest a possible relationship with Palaeoctonus. 



Everything in the structure of the form so far studied indicates 

 a well-muscled creature light in weight, possibly bipedal in gait 

 occasionally, and most assuredly swift in movement. The name 

 Poposaurus gracilis is suggested for the material herein described 

 from its discovery on the Popo Agie river. 



The type specimen is numbered 602 in the University of Chicago 

 collections. It was collected by Professor E. B. Branson in the 

 red beds near Lander, Wyoming. 



' "Notice of Some New Reptiles from the Upper Trias of Wyoming," Jour. Geol., 

 XII (1904), 688. 



