Moodie, Kans. Univ. Sci. Bull., VI, No. 2, p. 341, pl. 2, fig. 3; pl. 8, fig. 4; pl. 9, fig. 2; pl. 10. 1912. The remains on which the present species is based are inclosed in a much fractured nodule. The parts of the animal which have been identified are: a part of the skull and left mandible, two clavicles, a humerus, impressions of several vertebræ, a portion of the dorsal region of the body with several ribs, two portions of the caudal region with several ribs and unidentified fragments. (Plate 4, fig. 3.) The animal, from the shape and form of the ribs, is undoubtedly a branchiosaurian, since short, heavy, straight ribs have not yet been found to be associated with other than branchiosaurian structures. It is placed in the genus Mazonerpeton on account of the structure of the pectoral elements, the form of the humerus, and the length of the tail, all of which agree in structure with _Mazonerpeton longicaudatum_. The animal attained, perhaps, a length of 4.5 inches, while that of _M. longicaudatum_ was about 3 inches. The tail in the present species is very long and slender, more elongate than in any other known branchiosaurian. [Illustration: Fig. 14_b_. Skeleton of _Mazonerpeton costatum_ Moodie. × 1.5. Original in Yale University Museum, _dv_, dorsal vertebra; _ch_, neutral spines; _cl_, clavicle; _cv_, caudal vertebræ; _f_, femur: _h_, humerus; _m_, mandible; _rb_, rib; _sk_, skull; _v_, vertebræ.] The part of the skull preserved is very unsatisfactory and, aside from the fact that it seems to represent the under side of the left half of the skull, little can be said. Three sutures can be observed, but what sutures they are is undetermined. The left mandible lies crushed on the edge of the skull and partially obscures what little there is of that structure. The slightly curved impression, from which the bone has been either broken or weathered, measures 13 mm. in length by 3 mm. in posterior diameter by 1 mm. in anterior diameter. These measurements show the element to have been slender and pointed anteriorly. Very little accurate information can be derived from the study of the vertebral column of the specimen, nor can the dorsal vertebral formula be made out, since only a portion of the length of that region is preserved and only a few rather indefinite impressions can be discerned. These impressions show the vertebræ to be short and higher than in most Branchiosauria. The caudal series is represented by two sections, one of which is, apparently, from near the base of the tail, judging from the size of the caudal ribs preserved; the other is from near the tip of the tail, and shows the constituents to have been long and slender. Ribs are apparently absent on this section. The position of the two caudal sections shows that when the animal died it was coiled up much like a snake, so that in the fractured nodule three sections of the body are visible. The tail was probably half as long again as the body.