1884. ] Batrachia of the Permian Period of North America. 35 
sharper and of a net-like pattern. The neural spines are not so 
much expanded at the apex. It has been found in the Permian 
beds of New Mexico. The Æ. ferricolus Cope, is a still smaller 
species, known from skulls from Texas. This, with the Æ. mega- 
cephalus and the Trimerorhachis insignis, were found by Mr. Jacob 
Boll, a naturalist of Dallas, Texas, who was a man of many ac- 
complishments and an ardent explorer. He lost his life through 
Fic. 6.—Side view of skull of Eryops megacephalus, one-fifth nat. size. 
his indifference to his personal comfort while exploring the Per- 
mian beds at my instance. 
ACHELOMA Cope. 
This genus is allied to Eryops, and differs in two principal 
points. One of these is the 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 thus continuous. The other is the absence of the 
condyles of the humerus, a point in which it resembles, Trimero- 
thachis. The vertebral segments are more robust than in Trimero- 
the Js, and less so than in Eryops; and it agrees with those 
§enera in the absence of the mandibular angular process. 
The only known species of this genus is the A. cumminsi from 
€xas. Its structure is pretty well known. It resembles in gen- 
eral the Eryops megacephalus with its small orbits and absence of 
te groove, but is smaller and differs in various details. The 
skull is triangular, and measures a little more than seven inches 
ng by five wide, and has an open honeycombed sculpture of the 
Surface. The vertebrae and limbs are small for the size of the 
skull ; and in the former the summits of the neural spine are not 
