Large, terrestrial or amphibious vertebrata; skull bones deeply marked with pits and grooves which take the form of lateral-line canals; infra- and supraorbital canals, antorbital commissure, jugal canal, and occipital cross-commissure of the lateral-line system present in _Eryops megacephalus_ Cope; carpus and tarsus osseous; pubis an osseous plate, surrounded in life by a large amount of cartilage; fore and hind limbs pentadactyl; orbits, in the typical genus, located far back on the skull and near the median line; cleithrum present on the scapula; vertebræ rachitomous, the intercentrum supporting the arch in the dorsal region; parasphenoid well-developed or reduced; teeth on pterygoids, palatines, prevomers, and parasphenoid. Range: Upper Pennsylvanian to Permian. Distribution: America, Europe, Asia. =Genus ERYOPS Cope, 1877.= Type: _Eryops megacephalus_ Cope. Skull long, comparatively narrow; proportion of length to breadth about 9 to 7. Roof bones coarsely sculptured posteriorly, finely sculptured anteriorly. Nasals and premaxillæ very large; frontals excluded from the orbits by junction of pre- and post-frontals. Pterygoids not meeting in the median line; parasphenoid dagger-shaped, tapering gradually to a point just in front of the palatine foramen; prevomers large. Orbits subcircular, situated in the posterior half of the skull; nares subovate, remote, at a considerable distance from the tip of the skull. Many minute denticles, on pterygoids, palatines, prevomers, and parasphenoid. Teeth circular in cross-section, strongly ribbed near the base, dentine strongly infolded. Three large teeth on each palatine. Mandible without postcotyloid process. Vertebræ rachitomous. Ribs double-headed. Pubis osseous. Three species (Permian), _E. megacephalus_, _E. latus_, and _E. willistoni_, are assigned to the genus. Eryops is represented in the Carboniferous deposits of North America by incomplete vertebral remains described by Case (94) from near Pittsburgh, Pennsylvania. [Illustration: MOODIE PLATE 25 1. Photograph of type specimen of _Erpetosaurus_ (_Tuditanus_) _radiatus_ Cope, from the Coal Measures of Linton, Ohio. × 1.3. Original in American Museum of Natural History. 2. Photograph of type specimen of _Erpetosaurus tabulatus_ Cope, from the Coal Measures of Linton, Ohio. × 2. Original in the Zoological Collections of Columbia University. 3. Photograph of the impression of _Stegops divaricata_ Cope, from the Coal Measures of Linton, Ohio. × 2. The specimen figured is in the American Museum of Natural History. Its obverse is in the collections at Walker Museum, University of Chicago.