INTRODUCTION 3 



Certain morphological problems I have discussed in the following 

 pages, and I have given what seems to me to be the legitimate 

 conclusions regarding the immediate relationships of the forms under 

 discussion. The present work, however, is offered more as a con- 

 tribution to our knowledge of ancient reptiles and amphibians, 

 with such summaries and definitions, based chiefly on American 

 forms, as our present knowledge permits. The illustrations of the 

 work throughout are by myself. 



All the forms from the Texas deposits mentioned or described 

 in the following pages as of specimens which I have studied, come 

 from the upper or Clear Fork division. 



Mr. Cummins has recently given an annotated Ust' of the various 

 genera of the Texas Permian with their locaUties or horizons, 

 so far as could be obtained. My own experience quite confirms 

 his opinion that there is a distinction between the faunas of the 

 Wichita and Clear Fork divisions (no vertebrates are known, so 

 far as I am aware, from the Double Mountain division above the 

 Clear Fork, though footprints do occur in the shales of that division) . 

 The collections made by the University of Chicago expeditions in 

 Texas the past few years have been almost exclusively from the 

 Clear Fork division. These collections embrace, to the best of my 

 recollection, the following forms: 



Amphibia: Lysorophus, Diplocaulus, Trimerorhachis (appar- 

 ently absent from the upper part), Eryops, Cacops, Dissorophus, 

 Aspidosaurus, Cardiacephalus. 



Reptilia: from the uppermost beds, Labidosaurus, Naosaurus, 

 Dimetrodon; from lower horizons, Naosaurus, Dimetrodon, Clepsy- 

 drops, Varanosaurus, Trispondylus, Casea, Araeoscelis, Captorhinus, 

 Diadectes, Seymouria, etc. 



Perhaps the most characteristic of the upper beds is Labido- 

 saurus, of the lower, Cricotus, and their horizons may be known as 

 the Labidosaurus and Cricotus zones. On the other hand I feel 

 quite confident that no definite line can be made between the two 

 divisions, and at present Clear Fork can be used in a general way 

 to designate the upper, and Wichita the lower, part of the Texas 

 deposits. 



■ Journal of Geology, XVII (1908), 737. 



