Fig. 16_a_. Nearly complete specimen of _Cocytinus gyrinoides_ Cope, from the Coal Measures of Linton, Ohio. Original in the American Museum of Natural History. × 0.95. Measurements (No. 2564, American Museum of Natural History). mm. Length of entire specimen 113 Length of skull 15 Width of head posterior 15.5 Length of vertebra 2 Length of rib 4 =Genus ERIERPETON Moodie.= Moodie, Kans. Univ. Sci. Bull., VI, No. 2, p. 328, 1912. Type: _Erierpeton branchialis_ Moodie. The generic characters are found, first of all, in the presence of hyobranchial arches which indicate its relationship to the formerly described _Cocytinus gyrinoides_ Cope, from Ohio. The only other known extinct genera of Caudata which possess, or at least have preserved, the hyobranchial arches are the Jurassic _Hylæobatrachus_ from Belgium and Lysorophus from the Permian of Texas. The present form is widely distinct from both of these genera in the shape of the mandible and the form and arrangement of the hyobranchial bars. The genus _Erierpeton_ finds its closest ally in _Cocytinus_, in the family Cocytinidæ, which possibly belongs in the order Caudata and the suborder Proteida of Cope. =Erierpeton branchialis Moodie.= Moodie, Kans. Univ. Sci. Bull., VI, No. 2, pp. 329-330, pl. 1, fig. 3; pl. 2, fig. I, 1912. Type: Specimen No. 801 (222) 5, Yale University, Museum. Horizon and locality: Mazon Creek shales, near Morris, Illinois. The amphibian remains designated by the above name consist of a distinct mandible and some rather indefinite body impressions (plate 3, fig. 4). Three elongate impressions occur between the rami of the mandibles (fig. 15, A), which, I suppose, must represent hyoid bones belonging to the hyobranchial arches. The lateral elements are paired and the median impression is straight and lies between the paired impressions of the hyoids. The paired portions probably represent the hypohyals or hypohyals plus the ceratohyals, and the unpaired portion of the first basibranchial, according to the nomenclature of Wiedersheim (Comparative Anatomy of Vertebrates, 1897, p. 86). If the impressions have been correctly interpreted the present specimen is of very great interest, since it is the first evidence we have of the hyobranchial arches in the Amphibia of Mazon Creek, and the second in the Carboniferous of North America. Dawson doubtfully identified (216) some elements of the Joggins Amphibia as hyoids, but was uncertain as to their position. Cope described fully the well-developed hyobranchial apparatus of _Cocytinus gyrinoides_ (123) from the Coal Measures of Ohio. Among other Paleozoic Amphibia Williston (614) has described branchial arches in the peculiar form _Lysorophus tricarinatus_ Cope, from the Permian of Texas.