90 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



is pierced by an enteplcondylar foramen. From the outer side of the distal 

 end a sharp ridge runs up the ventral face nearly to the proximal end. 



This is the single case among the Amphibia from the Texas Red Beds, 

 or their equivalent elsewhere, in which an enteplcondylar foramen has been 

 found in the humerus. The opening in the humerus of Acheloma cumminsi 

 is purely accidental in the opinion of Williston, Broom, and the author. 

 For this reason it is possible that the humerus may be reptilian and in acci- 

 dental association. 



The femur is more slender than the humerus, with the proximal and 

 distal ends subequal and only moderately expanded. A thin high crest in 

 the posterior surface occupies the middle three-fifths, reaching to neither 

 extremity. The lower end is bent strongly backwards, so that the articular 

 surface looks somewhat backwards as well as downwards. The whole bone 

 recalls that of Eryops. 



Fragments of the tibia, fibula, and metapodial bones have also been dis- 

 covered, but little can be made out concerning them. Limbs such as are 

 indicated by these bones would have been very short and practically useless 

 to the animal, being clearly degenerate. The posterior limb was even more 

 reduced than the anterior. 



Diplocaulus, in the flesh, must have been one of the most curious crea- 

 tures of its time. The body was fairly short and heavy; the flat, triangular 

 head very disproportionate in size, and the limbs weak and almost useless. 

 The greatest number of vertebrse known is twenty, but if we add one-half 

 more the body of the animal must still have been absurdly rotund and 

 stubby. It is probable that the animal could not raise its enormous head 

 from the ground except by a short, paroxysmal effort. The head must have 

 been pushed forward through the slime and mud at the bottom of some 

 small body of water, as the animal fed on small, slow-moving creatures 

 or vegetation. There is no hint of the use of the enormous horns; it has 

 been suggested that they protected external gills, but there is no reason to 

 assume the presence of external gills except the pit, which lies on the lower 

 surface of the horns posterior to the pterygoid. It is more probable that 

 these animals were under the influence of the same conditions which caused 

 the development of excessive structures in contemporaneous reptiles and 

 amphibians. Jaekel's suggestion (56) of the derivation of Diplocaulus from 

 forms like Ceraterpeton and Diceratosaurus is very probably correct. 



The position of Diplocaulus is uncertain. In many particulars it re- 

 sembles the Microsauria, but departs radically from the order in others. 

 In the skull and complete vertebrae the connection with the Microsauria 

 is strongly indicated, but, as pointed out by Williston, the ribs are notably 

 different. The Microsauria have single-headed ribs attached interverte- 

 brally; but in Diplocaulus the ribs are two-headed and are attached to intra- 

 vertebral diapophyses and parapophyses. Williston (70) believes that this 

 is a sufficient reason for placing Diplocaulus in a group of higher than family 

 rank, but hardly sufficient to exclude them from the order Microsajiria. 

 He is inclined to attach rather more weight to the method of rib articulation 

 than is usual. Moody (61) would place Diplocaulus in a distinct new order, 

 Diplocaulia, which he places doubtfully in a subclass Holospondyli, thinking 

 that it may belong in the Stegocephalia. Since Diceratosaurus Jaekel appears 

 to connect, in many ways, the undisputed Microsaurian Ceraterpeton with 

 Diplocaulus, I have retained the latter as a family of the Microsauria. 



