RHACHITOMOUS VERTEBRAE 589 



Permian that I knew hitherto, and I know no less than twenty 

 different forms of Permian humeri. It is that of one of the smallest 

 of known Permian reptiles, Pleiiristion Case, belonging in the 

 Pariotichidae. As will be seen, however, the expansion of the 

 extremities is great, though the shaft is slender. In the same 

 plate (Fig. 3) I give a figure of the humerus of Sphenodon punctatus 

 for comparison. It will be observed how clumsy the bone is in 

 comparison with that of Araeoscelis. For comparison's sake I 

 figure the humeri of Pleuristion and Sphenodon twice natural size. 

 The concurrence of an entepicondylar foramen and an ectepi- 

 condylar groove is found in the pelycosaurs, but the groove is 

 never converted into a foramen. That the presence of a foramen 

 in the present genus is of great phylogenetic significance I do not 

 believe. 



The same slenderness is characteristic of the femur and leg 

 bones. In Plate I, Figs. 7 and 8, I give, enlarged one-half for the 

 sake of comparison, illustrations of a femur of one of the numerous 

 young specimens, specimens lacking the articular ossifications 

 and muscular markings. That it belongs with the same species 

 as does the larger bone shown natural size in Figs. 9 and 10 there 

 can be no doubt, notwithstanding the apparent differences, since 

 about a dozen femora of various sizes are present in the collection, 

 as also many humeri of various degrees of ossification and size. 

 In the side view will be seen the remarkable sigmoid curvature 

 so characteristic of the bone. The adult bone shows sharply 

 defined the articular surfaces for epipodial bones, and, proximally, 

 the well-developed, rounded head and trochanter. The shaft is 

 proportionally somewhat stouter than is that of the juvenile bone, 

 and the extremities are more sharply expanded. The tibia and 

 fibula are extremely slender, very nearly or quite the full length of 

 the femora; the tibia has a well-developed and protuberant 

 cnemial process, better developed than I have observed in any 

 other Permian vertebrate. The metapodials are likewise very 

 slender, those of the hind feet apparently more so than those of the 

 front feet, as are also their phalanges. I hope to be able in a later 

 communication to give the complete or nearly complete structure 

 of the hind extremities at least. The claws are slender and 



