250 S. W. WILLISTON NEW GENERA OF PERMIAN VERTEBRATES 



Page 

 Taxonomy 277 



Dissorophus multicinctus ." . 277 



Dissorophidse — family new 277 



General characteristics 277 



Genus Dissorophus Cope 278 



Genus Cacops Williston 278 



Trematopsidse — family new 278 



Restoration 278 



Desmosponclylus anomalus — geuus and species new 280 



Explanation of plates 283 



Introduction 



character of the permian beds of northern texas 



In a field experience dating from July, 1874, in nearly every known 

 vertebrate horizon of North America, I know of no beds so difficult of 

 exploitation as those of the Permian of northern Texas. As a rnle the 

 vertebrate fossils are found more or less broken and weathered, scattered 

 about on the sloping exposed surfaces. Occurring as the bones do, almost 

 invariably concealed beneath a thin or thick covering of cemented matrix, 

 so like the color and form of the countless millions of nodules, it is only 

 wlien they have been broken up and weathered by exposure that the slight 

 colorational differences presented by the fractured surfaces distinguish 

 them. It thus happens that by far the larger part of the material se- 

 cured, especially that of the smaller animals, is more or less fragmentary 

 in character, though fortunately preserved from rapid disintegration by 

 the covering of more or less intractable matrix. 



CONDITIONS OF FOSSILIZATION 



The middle portion of the deposits is to a large extent free from nodu- 

 lar concretions, presenting smooth, clean surfaces of red clay, especially 

 inviting to the collector. But, unfortunately, it is these attractive de- 

 posits which are the most barren of fossils. I have searched patiently 

 over such beds for many successive hours without being rewarded by a 

 single fragment of a fossil ; and it is for this reason that one, after a 

 little experience, learns to avoid these clay deposits, or gives them but 

 scant attention. Nevertheless it is in these "barren" deposits that the 

 prizes of the Texas Permian are to be sought. When fossils do occur in 

 them, they usually are excellently preserved and largely free from the 

 exasperating matrix. Professor Case has observed that but one or two 

 specimens may be expected from these clay beds in a season's work, and 



