SYSTEMATIC REVISION 35 



"Mandible without angular process. Teeth of the jaws subequal, rather 

 larger anteriorly; some large ones on the os palatinum at different points 

 along the external margin. Pterygoid bone ending in a free, decurved edge 

 anterior to the quadrate bone. Palatines and pterygoids narrow, leaving 

 a wide palatal foramen. Vertebrae in their principal features as in Eryops. 

 The humerus is unlike any of those enumerated in my synopsis of Permian 

 humeri, but resembles the one figuied by Gaudry as belonging to Actinodon, 

 except that in Acheloma there are no condyles and there is an epicondylar 

 foramen. This is the first time I have observed the foramen in a Bairachian, 

 though it is universal, so far as known, in the Pelycosauria. As in Actinodon, 

 there is a short process above the external epicondylar angle. 



"The absence of humeral condyles in this genus is paralleled by the same 

 feature in Clepsydrops natalis. It looks as though the animal were young 

 and had not yet attained to the coossification of epiphyses. This theory 

 may account for the condition of the humeri in the two species mentioned. 

 It occurs equally in the Trimerorhachis insignis. As all these species show 

 every other indication of maturity, and as I have never yet observed free 

 epiphyses in any of my numerous Texan collections, I am disposed to look 

 on this condition of the humeri as a case of permanent incompleteness, of 

 which the Batrachia present so many instances." 



In the second paper Cope's description is as follows: 



"The genus is allied to Eryops, and differs in two principal points. One 

 of these is absence of the lateral border of the cranial table formed by the 

 external side of the os intercalare in Eryops and various other genera, the 

 posterior outline of the skull being continuous. The other is the absence 

 of the condyles of the humerus, a point in which it resembles Trimerorhachis. 

 The veitical segments are more robust than in Trimerorhachis, and less so 

 than in Eryops; and it agrees with those genera in the absence of the man- 

 dibular, angular process. 



"The only known species of this genus is the A. cumminsi from Texas. 

 Its structure is pretty well known. It resembles in general the Eryops mega- 

 cephahis with its small orbits and absence of lyrate groove, but is smaller 

 and differs in various details. The skull is triangular and measures a little 

 more than seven inches long by five wide, and has an open honeycombed 

 sculpture of the surface. The vertebrse and limbs are small for the size of 

 the skull; and in the former the summits of the neural spines are not 

 expanded." 



Acheloma cumminsi Cope. 



Proc. Am. Phil. Soc, vol. xx, 1882, p. 455. 



Type: The same as the genus. 



Original description: "This animal is represented by a greater part of a 

 skull and vertebral column, with both humeri and scapula and various 

 other bones of the limbs, includ ng phalanges. All of these remains look a 

 good deal like Eryops megacephalus, and they might be supposed on hasty 

 examination to belong to the young of that species. On a full investigation 

 the following differences appear, besides those already mentioned in the gen- 

 eric diagnosis: 



"The muzzle is relatively much shorter and the extremity is less 

 depressed; the length from the supraoccipital forwards is a little less than the 

 total width at the same point. In agreement with this, the mandibular rami, 



