108 PROCEEDINGS OP THE ACADEMY OF [1883. 



ON SOME VERTEBRATA FROM THE PERMIAN OF ILLINOIS. 

 BY E. D. COPE.. 



The first notice of the existence of the Permian formation in 

 Illinois was published in these Proceedings for 1876, p. 404, et 

 seq. I then described the genera, Gricotus and Clepsydrops, and 

 a species of fish allied to Ctenodus. In the Proceedings of the 

 American Philosophical Society for 1877 (commencing at p. 52), 

 I added descriptions of other species, and in a second paper in 

 the same volume, p. 182, 1 showed that the entire number known to 

 that date was seventeen. Since then Mr. William Gurle^', of 

 Dansville, 111., has sent me some additional specimens, which 

 increase our knowledge of this interesting fauna. 



A tooth in the collection is an incisor of a species of the Diadeo- 

 tidee^ a family not hitherto recognized in Illinois, although I have 

 recorded it from Texas and New Mexico. It is more slender than 

 the corresponding teeth of any of the species known to me. I do 

 not know the incisors of the GMlonyx rapidens. I note here that 

 thegenus PhanerosaurusvoxiMeyer^from the Permian of German}'^, 

 probably belongs to the Diadectidae or the Bolosauridse. The 

 vertebrae are a good deal like those o£ JEmpedias,^ but apparently 

 lack the hyposphen. 



Didymodus C?) compressus Newberry. Diplodus (?) compressus Newb. Cope, Pro- 

 ceeds. Amer. Philos. Soc, 1877, 5.3. 



The name Diplodus was used by Rafinesque for a valid genus 

 of fishes before it was employed by Agassiz for the present genus. 

 I therefore propose to substitute for it the name Didymodus. 

 Thoracodus emydinus gen. et .=p. nov. 



Char. gen. — The form of the tooth or jaw on which this genus 

 is proposed, reminds one of that of a Diodon, and also of one-half of 

 that of a Janassa. It appears to be the half of a bilateral plate, which 

 is divided on the middle line by suture. Its form is somewhat 

 that of the anterior part of an episternal bone of a tortoise. It 

 consists essentially of a smooth border, separated from the 

 remainder of the tooth by a transverse groove. The interior 



^ Mittbeilungen a. d. Koeniglicli. Mineral., Geolog. u. praehistor.- 

 Museum, Dresden ; V, Nachtrage zur Dyas ; Geinitz und DeiclimuUer, 

 1882, p. 10. 



