578 Williston — New Genera of Permian Reptiles. 



Omitting the few doubtful genera there are to-day in the 

 collections not less than sixty distinctly differentiated genera 

 from the Permian deposits of Texas, Oklahoma, Kansas, New 

 Mexico, Illinois and Pennsylvania, distributed about equally 

 among the Amphibia, Cotylosauria and Theromorpha. They 

 have been classified under at least twenty-three families, and 

 ten larger groups. 



As regards the distribution of these genera, twelve are 

 known only from New Mexico, two from Oklahoma, two from 

 Illinois, and two from Pennsylvania. Four genera are more 

 or less doubtfully common to New Mexico and Texas, and four 

 to Illinois and Texas. The four genera supposed to be com- 

 mon to New Mexico and Texas are Eryops, Aspidosaurus, 

 JEdaphosaurus and Diadectes, but it is probable that some 

 of these, if not all, will be found to be distinct when 

 more thoroughly known. The four genera common to 

 Illinois and Texas are Zysorophus, Diplocaulus, Cricotus 

 and Clepsydrops, the first three almost certainly ; the last 

 doubtfully the same. Not a trace of any one of these has 

 been detected in New Mexico, of the first three not even 

 their families, though it is possible that Chenoprosopus may 

 be allied to Cricotus. Some of the most common genera 

 in Texas are utterly unknown in New Mexico, notably Dime- 

 trodon, Captorhinus, Labidosaurus, Diplocatdus, Lysorcphus 

 and Trim,erorhachis, and only the first of these is replaced by 

 an allied form, Sphenacodon, so far as we know ; while Thero- 

 pleura of Texas is represented by the closely allied but distinct 

 Ophiacodon ; Diadectes, Diadectoides and Chilonyx by No- 

 thodon, Animasaurus and Diasparactus / Zatrachys by 

 JPlatyhystrix, etc. The genus Limnoscelis has no known 

 allied form. Not a single one of all these American genera 

 has been recognized elsewhere, though I am convinced from 

 the examination of European specimens, as also from Huene's 

 studies, that some of the known European forms are allied, 

 possibly belonging in identical genera. Especially have m I 

 seen a part of a spine in the museum at Halle which I could 

 not distinguish from the peculiar ones of Edaphosaurus ; and 

 long-spin ed, dimetrodont forms seem also to occur there. 

 Broom and Watson have urged the relationships of some of 

 the south African types with certain ones of America, and 

 their arguments are persuasive; nevertheless, the relationships 

 of the South African forms do not seem to be as close as do 

 some of the European Permian genera. Perhaps, after all, as 

 Case has urged, we are dealing chiefly with generalized rather 

 than genetic characters. 



That deposits no thicker than those of Texas and New 

 Mexico should have already yielded so extraordinarily rich a 



