82 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



Table V — Continued. 

 Achehma: 



1. Small, not exceeding 500 centimeters in length. 



2. Otic notch absent. 



3. Orbits of medium size; in the middle of the skull. 



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



5. Angle of the lower jaw not produced beyond the quadrate. 



6. Lower jaw proportionately as wide, vertically, as in Eryops. 



7. Skull with a moderately fine sculpture of pits, uniform in size and distribution 



over the skull, except at anterior end of the jaws, where it is absent. 



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



9. Unknown. 



10. Unknown. 



11. Ribs flattened, expanded at proximal and distal ends but without extension 



of the posterior edge. 



12. Unknown. 



13. Unknown. 



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



a dorsal plate. 



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



ends. 



16. Unknown. 



17. Unknown. 



Table VI. Contrasting the Characters of the Genera of the Trimerorhachidce. 



Trimerorhachis: 



1. Small, not exceeding 500 centimeters in length. 



2. Skull elongate, flat, orbits small, in anterior half of the skull; without elevated 



•rims; no interorbital depression. 



3. Nares not terminal, but near anterior end. 



4. No preorbital depressions. 



5. Sculpture finely reticulate; edges of skull smooth. 



6. Tabulare not prolonged into points. Posterior edge of skull not deeply concave. 



7. Occipital condyle single. 



8. A double row of teeth on maxillary. Teeth not enlarged except on the mandible 



and the palatine (?). 



9. Intercentra thin, not constricting the notochord. 



Zatrachys: 



1. Small, not exceeding 500 centimeters in length. 



2. Skull less elongate; elevated in orbital region; orbits in the posterior third of 



skull, surrounded by prominent rims; a strong interorbital depression. 



3. Nares far back. 



4. Deep preorbital depressions. 



5. Sculpture not certain, surface destroyed in specimens preserved. Sutures very 



complicated, long processes from the edges of the bones interlocking strongly. 



6. Tabulare prolonged into points. Posterior edge of skull more deeply concave. 



7. Occipital condyle divided. 

 Only the skull known. 



Table VII. Contrasting the Characters of the Genera of the Dissorhophidee. 

 Dissorhophus. 



1. Small, not exceeding 500 centimeters in length. 



2. Skull not elongate, elevated, resembling in general proportions that of Diadectes. 



Orbits large, in the middle of skull, looking laterally. Otic notch closed, form- 

 ing a fenestra. 



3. Nares nearly terminal. 



4. Parasphenoid a slender rod. 



j. One tusk on each prevomer and palatine. Maxillary and mandibular teeth 

 small, sharply conical. 



