mm. Length of tail as preserved 105 Length of anterior vertebra 1.5 Diameter of anterior vertebra 1 Length of rib 5 Width of rib 1 The above-described specimen represents what I suppose to be the posterior part of the body of _Pleuroptyx clavatus_ Cope. The characters of the ribs and vertebræ are the same. The fragment is interesting, since it gives an insight into the form of the body, which was slender, conforming thus to other long-tailed microsaurs. Length of specimen, 65 mm.; width of specimen, 30 mm. There is still a third example of this species among the collections belonging to the National Museum (No. 4484). The specimen includes a badly crushed posterior portion of a skull and a series of about 16 crushed vertebræ, with several pairs of ribs and ventral scutes. Very little can be said of the skull save that the maxilla of the right side was long and bore from 15 to 20 teeth, of which 9 are preserved more or less completely. The mandible is likewise crushed and one can not determine its elements. Portions of 2 or 3 teeth are preserved. The form of the mandible is long and slender. The ventral scutes are of the pectoral region. They are long, slender, and thread-like. They are not closely packed, but I count 12 in a distance of a millimeter. So far as can be determined the vertebræ are the same as has been described for other specimens. They are short and heavy. The ribs show, for the most part, the same characters as the type specimen. Measurements of Third Specimen (No. 4484, U. S. Nat. Mus.). mm. Length of specimen 60 Length of preserved portion of skull 15 Length of tooth 25 Posterior width of mandible 3 Length of anterior Vertebra 2 Length of rib 4 Width of rib 1 =Genus PHLEGETHONTIA Cope, 1871.= Cope, Proc. Am. Phil. Soc., p. 177, 1871. Cope, Geol. Surv. Ohio, II, pt. II, p. 366, 1875. Type: _Phlegethontia linearis_ Cope.