4. Type and only known specimen of _Micrerpeton caudatum_ Moodie, a branchiosaur from the Coal Measures shales of Mazon Creek, Illinois. × 2. Original in collections at Walker Museum, University of Chicago. ] =Eryops sp. indet. Case, 1908.= Case, Annals Carnegie Mus., IV, p. 234, pl. 59, 1908. A dorsal vertebra is very probably from this genus. The specimen consists of a nearly perfect vertebra, lacking only the anterior zygapophysis and the upper portion of the neural spine (plate 18, fig. 2). It shows no character that would warrant its separation from the genus, and indicates a medium-sized individual. The zygapophyses have clean-cut articular faces. The pleurocentra are thickened above, with just well-defined articular faces, which were applied to faces on the neural arch posterior to the origin of the transverse process. The intercentrum is of the familiar halfmoon-shape, thick and heavy below, and thinner toward the extremities; the anterior edge is marked near the top by the indentation found on the intercentra of _Eryops_. Height of the vertebra from the middle of the lower face of the intercentrum to the middle of the neural canal, 0.035 m.; width of intercentrum 0.026 m. The second recognizable specimen is a neural spine from the caudal series. This is without question a portion of the skeleton of an Eryops. Similar spines were described by Cope as _Eryops (Epicordylus) erythrolithicus_, but later discoveries seem to show that similar characters occur in other species of the genus as well. The apex of the spine is bifurcate; the space between extremities is concave and perfectly smooth; below the sides of the spine are rather rugose and marked with ridges. The lower portion of the spine is elongated anteroposteriorly and the edges are marked with sharp, double ridges. Three ribs also belong, in all probability, to the genus _Eryops_. The head of each rib is broad and the articular edge is divided between two faces which meet at an angle somewhat greater than a right angle; the two faces are continuous. The shaft is somewhat flattened and in the undistorted specimens is gently curved. The length of the largest rib is about 0.07 m. Other than these specimens there are several small intercentra (94) and the neural spine of a caudal vertebra from some undetermined amphibian. =Family MACRERPETIDÆ Moodie, 1909.= Moodie, Bull. Am. Mus. Nat. Hist., XXVI, art. XXV, p. 354, pl. lix, fig. 1, 1909.