S. W. WILI/ISTON NEW GENERA OF PERMIAN VERTEBRATES 



between several of the centra. Eelatively, as compared with the centra, 

 these intercentra are the largest known in any vertebrate, suggesting im- 

 pressively 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. (See plate 10, figure 3, and plate 16, 

 figures 8-12.) 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 distinct 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 disklike 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 men- 

 tioned above. 



Not only are the vertebrae so curiously intermediate between the ordi- 

 nary 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 (plate 16, figure 1) 

 is extraordinarily stout and rugose for its length. Immediately below 

 the lateral process there is a stout process, hitherto characteristic of cer- 

 tain temnospondylous amphibians, which I have called the ectepicondylar 

 process, most characteristically seen in Eryops and Euchirosaurus. No 

 such process is known in any Permian reptile, certainly in no Coty- 

 losaurian. Furthermore, the median process is developed into a stout 

 protuberance, quite as in Eryops. On the other hand, there is an entepi- 

 <^ondylar foramen, remarkable for its large size, known only among 

 amphibians in Diplocaulus and Cochleosaurus, wholly unrelated forms. 



The femur (plate 16, figures 4, 5) 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 extra- 

 ordinary 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 

 characters, though remarkably stout and robust (figures 2, 3). 



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 



