The limb is appropriate in its proportions to the present species, and may be described in this place. The first segment is one-third longer than the second, and has a transversely expanded head. The shaft is stout, the distal extremity not expanded and concave. The second segment is stout, more expanded proximally than distally, the proximal end truncate and slightly concave. A bone, much displaced, lies near it, and is probably ulna or radius; it is as stout as the first, the end not expanded. Of metatarsals there are 2, three-fifths the length of the second bone of the leg, and of phalanges 2, of 2 digits each. The proximal are three-fourths the length of the metatarsals, and indicate elongate toes. The obverse of the specimen is preserved, and contains no additional toes or phalanges. [Illustration: Fig. 33.--Forelimb of a member of the Molgophidæ, possibly Pleuroptyx clavatus Cope. × 0.75.] Measurements of the Type of Pleuroptyx clavatus Cope. mm. Length of vertebral centrum 14 Depth of a vertebral centrum 9 Depth of entire vertebra 22 Length of neural spine 8 Height of a neural spine 6 Length of a rib on the curve 42 Width of a rib at ala 9 Width of a rib at extremity 5 Length of first segment of leg 38 Length of second segment of leg 24 Length of metapodial bone 10 Length of first phalanx 7 Hitherto only two portions of the dorsal series and a left limb have been assigned to this species. The present specimen (No. 4479, U. S. Nat. Mus.) thus proves of interest in determining that the creature was long-tailed, like _Œstocephalus_, _Ptyonius_, and _Phlegethontia_, but unlike the first two genera the neural and hæmal spines are not elongate nor marked with radiating lines. The neural spines are indistinct and if developed at all were very low and short. The centra are short, cylindrical, and thick. They gradually decrease in size to where they are lost, since the portion preserved does not represent the entire length of the tail. There may have been 15 more vertebræ distally and 5 more proximally, thus making about 75 caudal vertebræ, as Woodward (630) has determined obtains in _Ceraterpeton galvani_ Huxley. The ribs are continuous throughout the length of the tail preserved and have precisely the same structure as is found in the dorsal region with the possible exception that the posterior alar expansion is not so well developed in the caudal ribs. The ribs are decidedly fan-shaped and articulate by a single head with a short transverse process. They are distinctly curved like all microsaurian ribs. Measurements of Specimen of Pleuroptyx clavatus Cope. (No. 4509, U. S. National Museum, Linton, Ohio, Coal Measures.)