NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 



127 



as the body was shoved forward on the ground. The thoracic ribs were some- 

 what expanded, as in several amphibians of the same fauna, probably as a 

 partial protection against some prowling Dimetrodon, which would have had 

 Eryops at a decided disadvantage if the encounter took place upon the land. 



Undoubtedly Eryops spent much of its time in the water, and found there 

 its chief food supply. The position of the eyes and nostrils near the top of 

 the skull shows that it could, and probably did, lie nearly submerged in the 

 water until the approach of some fish or small amphibian or reptile was 

 sufficiently close to warrant a sudden rush with its enormous jaws distended, 

 and by a sudden snap drive home the powerful tusks, from which there was 

 no escape. 



No coprolites have been definitely associated with the skeletons of 

 Eryops, but large ones occurring in great abundance in the same beds con- 

 tain remains of fishes and small bones of other vertebrates. 



The bones of this animal are among the most common in the Texas and 

 Oklahoma beds, and have been found in Kansas, Illinois, and Pennsylvania. 

 Evidently the genus was represented by numerous individuals and was 

 widely spread over the continent. 



Closely related to the Eryops were Parioxys and Anisodexis, known only 

 from the skulls, but while they were probably of similar form and habits, they 

 were smaller and possibly more active. It is probable that fuller knowledge 

 of the fauna will record many more forms 

 related to this genus, and may prove that 

 forms known from areas as widely sepa- 

 rated from the Texas locality as New Mex- 

 ico, Illinois, and Pennsylvania should be 

 placed in distinct genera. 



Acheloma. — This genus is known only 

 from the skull, a part of the pectoral girdle, 

 ribs, humerus, and an incomplete vertebral 

 column. We may not as yet attempt a 

 restoration or hazard a guess at its habits. 

 The peculiar form of the scapula-coracoids 

 is undoubtedly associated with some activ- 

 ity which we can not surmise. The anterior 

 ribs are expanded distally , probably for pro- 

 tection against some active predatory form. 

 1 1 probably did not exceed 800 mm . in length . 



Trimerorhachis (fig. 14). — The genus is known only from the skull and a 

 few vertebrae. Some limb and girdle bones have been assigned to the genus, 

 but only tentatively. It is unfortunate that more is not known of Trimero- 

 rhachis, for it is one of the most primitive amphibians in the fauna. The skull 

 is longer than wide, with the nostrils at the anterior end and the eyes in the 



Fig. 14. — Restoration of the head of Trimero- 

 rhachis sp. About one-half the size of an 

 average specimen. 



