mm. Length of scapula 14 Distal width 6 Proximal diameter 3 Length of clavicle (?) 24 Length of humerus 25 Length of ulna 24 Proximal width 4 Diameter of shaft 2 Distal width 3 Length of radius 25 Proximal width 4 Diameter of shaft 3 Width of distal end 4 =Genus PLEUROPTYX Cope, 1875.= Cope, Geol. Surv. Ohio, II, pt. II, p. 370, pl. xlii, fig. 1; pl. xliv, fig. 2, 1875. Cope, Proc. Phila. Acad. Nat. Sci., p. 16, 1875. Moodie, Proc. U. S. Nat. Mus., 37, p. 27, 1909. Type: _Pleuroptyx clavatus_ Cope. The specimens on which the species of this genus repose do not exhibit crania. The 5, probably 6, specimens which represent them offer various views of the vertebral column, and in none is there any trace of ventral or thoracic armature. Limbs can be ascribed to them with probability only. The vertebræ are of moderate length, with well-developed zygapophyses, and a short and not very elevated neural spine in the dorsal region, which is not sculptured in any way. The generic character is seen in the ribs. These are rather short and very stout and support an ala on the posterior or convex border, which expands downwards, and then suddenly contracts to the shaft. The extremity of the latter is broad and truncate, and includes a medullary cavity, which is only partially fitted with cancellated tissue. =Pleuroptyx clavatus Cope.= Cope, Geol. Surv. Ohio, II, pt. II, p. 370, pl. xlii, fig. 1; pl. xliv, fig. 2, 1875. Cope, Proc. Phila. Acad. Nat. Sci., p. 16. 1875. Moodie, Proc. U. S. Nat. Mus., 37, p. 27, 1909. Type: Specimen No. 8617 G, American Museum of Natural History. Horizon and locality: Linton, Ohio, Coal Measures. The general appearance of the species of Pleuroptyx is that of the Molgophis, so far as known, but nothing resembling the peculiar structure of the ribs is seen in any other. There is no assurance that the genus is distinct from Molgophis. Parts of two individuals express the typical characters of this species, while a third only differs in being considerably smaller. A fourth may very probably be referred here, and another, bearing several elements of a leg, should be most likely associated with the last mentioned. The ribs are considerably narrowed near the head, and appear to possess a low tubercular process some distance below it. The shaft is curved throughout; the laminar expansion is quite thin; while the distal end is expanded and concave, perhaps for the attachment of cartilage, although no trace of this remains on the shale. The neural spines have short bases, oblique anterior and nearly straight posterior borders, with obtuse extremity. I perceive no essential difference in the smaller specimen, which is one-third less than the types.