THE MICROSAURIAN FAMILY MOLGOPHID^. 153 



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 excep- 

 tion 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.) 



mm. mm. 



Length of tail as preserved 105 Length of rib 5 



Length of anterior vertebra 1.5 Width of rib I 



Diameter of anterior vertebra I 



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 ver- 

 tebras 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 micro- 

 saurs. 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 pos- 

 terior portion of a skull and a series of about 16 crushed vertebrae, 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. Por- 

 tions 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 vertebras 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. mm. 



Length of specimen 60 Length of anterior vertebra 2 



Length of preserved portion of skull 15 Length of rib 4 



Length of tooth 25 Width of rib I 



Posterior width of mandible 3 



Genus PHLEGETHONTIA Cope, 1871. 



COPE, Proc. Am. Phil. Soc., p. 177, 1871. 

 COPE, Geol. Surv. Ohio, H, pt. n, p. 366, 1875. 



Type: Phlegethontia linear is Cope. 



This is one of the most interesting genera of the present series. It rests chiefly 

 on a single specimen of one species, which is not perfect, but which displays the 

 following characters: Head elongate-triangular; body and tail extremely elongate, 

 the dorsal vertebrae without ribs, and the caudals without dilated spines ; no ven- 

 tral armature nor limbs. As a great portion of the length is presented, and no ventral 

 rods or scales are visible, and as this character is confirmed by a second specimen, 

 it probably belongs to the genus. The pectoral shields are also wanting in the spec- 



