62 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



diap>ophyses posteriorly with double-headed ribs, it is not impossible that such was 

 the character of the ribs on this genus. 



"The anterior border of the pedicel, beginning low down, projects forward, 

 so that if two vertebrae were closely applied the arch would rest on two centra, though 

 chiefly on the posterior one, and, so far as I can determine from careful measure- 

 ments, this would be the case with the zygapophyses closely interlocked. 



"That this was not the condition ordinarily, however, is rendered certain by 

 the presence of extraordinarily large intercentra found in position between several 

 of the centra. Relatively, as compared with the centra, these intercentra are the 

 largest known in any vertebrate, suggesting impressively the lower half of the 

 pleurocentra of Cricotus. When in position they reach upward to the middle of 

 the centrum, and almost or quite touch the extremities of the arch. If the ribs 

 were double-headed the capitulum must have articulated with the upper ends of 

 the intercentra. These intercentra are narrower above, so that there is left a dis- 

 tinct free space between the upper parts of the adjacent centra in the horizontal 

 straight position of the column. When curved upward, however, the arches 

 would fill the interstice between the contiguous vertebrae, leaving a wedge-shaped 

 space below, filled with the intercentrum. Some of the centra preserved are hardly 

 more than half the diameter of the largest. They are evidently caudal vertebrae, 

 though no indications of chevrons have been discovered. Others are even more 

 disk-like than the ones figured, resembling so closely various centra attributed to 

 Cricotus from the Illinois deposits, that it is probable that they really belong in this 

 genus and are centra, rather than to Cricotus, especially so as they agree in size with 

 the femur mentioned above. 



"Not only are the vertebrae so curiously intermediate between the ordinary 

 reptilian type and the embolomerous type, but the limb bones, both humeri and 

 femora, were referred unhesitatingly to the amphibians before the vertebrae were 

 recognized. The humerus is extraordinarily stout and rugose for its length. 

 Immediately below the lateral process there is a stout process, hitherto characteristic 

 of certain temnospondylous amphibians, which I have called the ectepicondylar pro- 

 cess, most characteristically seen in Eryops and Euchirosaurus. No such process 

 is known in any Permian reptile, certainly in no Cotylosaurian. Furthermore, the 

 median process is developed into a stout protuberance, quite as in Eryops. On the 

 other hand, there is an entepicondylar foramen, remarkable for its large size, known 

 only among amphibians in Diplocaulus and Cochleosaurus, wholly unrelated forms. 



"The femur also is remarkably amphibian in character in the extraordinary 

 development of the adductor crest, a character known in no other Permian reptile. 

 The digital fossa is extraordinary for its extent and depth, reaching nearly to the 

 middle of the bone. The bones identified as tibia and radius (the former was 

 found close to the femur and ilium, the latter in the wash) present no peculiar char- 

 acters, though remarkably stout and robust. 



"Among the material in the wash are fragments of a small skull mingled with 

 Trimerorhachis skull material, but there is too much doubt of their reptilian charac- 

 ter to make it worth while describing them'until further evidence of their identity 

 is forthcoming. 



"That the present genus is not a pelycosaurian is, of course, evident; its rela- 

 tionships with the cotylosaurians are more apparent. Nevertheless, the great 

 differences in the structure of both vertebrae and limb bones from anything known 

 among either the diadectid or pariotichid types render the exact position of the 

 genus very doubtful. Possibly, as I have said, it may eventually turn out to be 

 congeneric with some one of the few forms in which the vertebrae and limb bones 

 are yet unknown, especially Pantylus." 



