I06 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



The ribs are single-headed and quite flat, with expanded distal and prox- 

 imal ends. They overlapped each other from before backwards, forming a 

 strong protection for the thorax. 



Abdominal ribs were present as narrow rod-like elements, resembling 

 those of Lahidosaurus. 



There are twenty-two vertebra in series and one attached to the skull; 

 the series is, therefore, not continuous with the skull and it ends anterior to 

 the sacrum. The spines are low and stout with a round or oval terminal 

 face, showing attachment to a cartilaginous or bony plate. The neuro- 

 centra carry transverse processes, which are rather longer in the cervical 

 and thoracic regions than posteriorly; the ends of the processes are elongate 

 and inclined downward and forward toward the intercentra, but do not 

 reach them. The zygopophyses are oblique. The pleurocentra are small 

 and the intercentra without any notch on the posterior edge, as in Eryops. 

 In the same region the rib-heads are nearly twice as long as the faces on the 

 transverse processes, and must have reached to the intercentra, but were 

 attached to it by cartilage. In the posterior dorsals, the face on the trans- 

 verse process extends downward and forward to the intercentrum, but the 

 rib does not seem to touch the intercentrum. The posterior zygapophyses 

 are more nearly horizontal and the whole vertebra longer. The lower sur- 

 face of the intercentra shows a reticulate sculpture, somewhat similar to 

 that of Diplocaulus. The edges of the zygapophyses are particularly prom- 

 inent, forming a well-marked line on the sides of the neurocentra; this is 

 one of the striking features of the specimen as a whole. 



The humerus is a miniature of that of Eryops, except that it lacks the 

 articular condyles. The two ends stand at an angle of 70° to 75° to each 

 other. The surfaces are flat and indicate the presence of a considerable 

 quantity of cartilage. The outer edge of the upper face is expanded trans- 

 versely like the head of a capital T; this corresponds to the prominent, trans- 

 verse process in the same position in the head of Eryops. The shaft is much 

 more slender than in Eryops, but there are similar processes on the lower 

 end. In correlation with the lack of condylar surfaces, there is no well- 

 developed head for the radius. The entepicondylar process is proportionately 

 as strong as Eryops, but the distal surface extends to its inner extremity. 

 The humerus of the right side has a perforation in the position of the entepi- 

 condylar foramen, but there is none in the left side. This opening has been 

 interpreted as an entepicondylar foramen, but in the opinion of Doctors 

 Broom and Williston and the author it is an accidental perforation, prob- 

 ably produced after death. 



The radius has a narrow, straight shaft with the two ends considerably 

 expanded. 



The ulna is slender and curved, with the upper end expanded, but 

 nearly straight, and not curved as in the reptiles. There is no olecranon 

 process. 



The measurements are given in the original description. 



Genus TRIMERORHACHIS Cope (page 39). 



Characteristic specimens: Nos. 4565, 4557, 4714, 4584, two specimens. 

 Am. Mus. 



The following description is drawn from several specimens. The skull 

 is rather elongate in the cranial region and very flat. The elongation is 



