POPOSAURUS GRACILIS, A NEW REPTILE FROM THE 

 TRIASSIC OF WYOMING 



M. G. MEHL 



University of Wisconsin 



Some time ago the writer mentioned a new form from the 

 Triassic of Wyoming and briefly described one of the vertebra/ At 

 that time it was hoped that the explorations in the western Trias 

 of the past season would bring to light something further con- 

 cerning this peculiar form. No additional evidence has so far been 

 disclosed, however, in the collections from Arizona and New 

 Mexico, and it is probably well at this time to describe more fully 

 the remains for the benefit of others who may be engaged in the 

 same field. 



The material herein described consists of an ilium, several 

 vertebrae from various parts of the column, two femora, a tibia, the 

 proximal end of a fibula, and several innominate fragments. All 

 are considerably crushed and broken. The leg bones are so flat- 

 tened that it is rather difficult to determine the true proportions. 



The ilium, as previously pointed out,^ is very similar to that 

 described by J. H. Lees^ as belonging to Paleorhinus Bransoni. 

 The condition of the bone suggests little distortion; still, upon a 

 comparison with the specimen described by Lees, it is evident that 

 the supra-acetabular flange has been somewhat depressed by 

 pressure. To all appearances the acetabulum is formed almost 

 entirely by the ilium. It is broad and deep and closely confined 

 above by the supra-acetabular flange. In preparing the specimen 

 what appears to be a foramen of perhaps 5 mm. in diameter was 

 exposed, running in and slightly upward from the upper acetabular 

 surface. It is barely possible, however, that this is simply a matrix- 



' M. G. Mehl, "The Phytosauria of the Rocky Mountain Trias," Jour. GeoL, 

 1914 (in press). 



^Op. cit., p. 159. 



3 "The Skull of Paleorhinus, a Wyoming Phytosaur," Jour. GeoL, XV (1905), 44. 



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