38 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



Revised description: 



1. Small, not exceeding 500 centimeters in length. 



2. Otic notch absent. 



3. Orbits of medium size, in middle of skull. 



4. Nares near lateral edge of skull, but not terminal. 



5. Angle of lower jaw not produced behind quadrate. 



6. Lower jaw proportionately as wide as in Eryops. 



7. Skull with a moderately fine sculpture of pits, uniform in all 



parts of skull, except at anterior end of jaws, where it is 

 nearly absent. 



8. Teeth subequal in size, some, in the premaxillaries, enlarged 



slightly. 



9. Unknown. 



10. Unknown. 



11. Ribs flattened, expanded at proximal and distal ends but with- 



out extension of posterior edge. 



12. Unknown. 



13. Unknown. 



14. Spines of dorsal vertebrae expanded as if in contact with dorsal 



plate. 



15. Humerus short, resembles that of Eryops but without well- 



formed articular ends. 



16. Unknown. 



17. Unknown. 



Family TRIMERORHACHID/E Cope. 

 Am. Nat., vol. xvi, 1882, p. 335; Am. Nat., vol. xvni, 1884, p. 29. 



Original description: In the first paper Cope proposed the order Rha- 

 chitomi to replace the Ganocephala and divided it into two families: 



"Occipital condyle concave, undivided Trimerorhachidce 



Occipital condyle divided into lateral condyles Eryopida" 



In the second paper he adds: 



"The two families of this order (Rhachitomi) are well distinguished by the 

 form of the basioccipital bone. In the Trimerorhachidae its condyle is simple 

 and concave, somewhat as in some fishes. The Eryopid^ have the two con- 

 dyles characteristic of the Batrachia generally. This difference might be 

 esteemed as of greater than family significance, but it is less considerable 

 than at first sight appears. The simple, cotylus-like, basioccipital bone of 

 the Trimerorhachidae is notched above, sometimes deeply, to receive the 

 apex of the notochord. A corresponding notch on the inferior edge would, 

 if present, divide the articulation into two surfaces, which would greatly 

 resemble the condyles of Eryops. The latter are flat and look partly towards 

 each other, and are evidently separated originally by the Jissura notochordcz." 



Revised description: 



1. Small. Not exceeding 500 centimeters. 



2. Occipital condyles united. 



3. Otic notch small. 



4. Parasphenoid large. Basioccipital not apparent. 



5. (Two functional sacral ribs?) 



6. No dermal armor on back. 



