g2 REVISION OF THE PELYCOSAURIA. 



attached to the sides of the vertebra by capitulum and tuberculum as described in 

 the morphological description of Dimetrodon doUovianus, No. ii2 University of 

 Chicago. They are rounded, thin, and not very long. 



The third presacral has the bottom line decidedly shorter and concave. The 

 lower edges of the articular faces of the centra are beveled, leaving wide spaces for the 

 intercentrum. This is the first of the vertebrae in which the neural spines are pre- 

 served. The neural arch is torn loose and displaced backward slightly, but the spine 

 is in nearly the natural position. The base of the spine is wide antero-posteriorly, but 

 it rapidly narrows to a slender cylinder, tapering to the apex. It is naturally curved 

 to the rear. The capitulum and tuberculum of the rib are united and fused with the 

 sides of the centrum. 



The /;-.?/ and second presacrals are much shortened antero-posteriorly, the spines 

 resemble those of the third and are of nearly equal height. The ribs are small, with 

 the capitulum and tuberculum no longer distinct and closely fused to the side of the 



vertebrae. 



The sacrals : There are three sacrals. The spines of all and the neural arch of 

 the third are lost. The centra are largely hidden by the crests of the ilia which are in 

 position, but it is seen that the ribs of the first two are ver}- strong. 



The caiidals : The tail was very long and slender. There are seventeen caudals 

 connected with the sacrum and many others which have been arranged as nearly as 

 possible in position. It is evident that there are remnants of at least two tails in the 

 lot, so the exact length can not be given. The first ten caudals bear ribs which are 

 short but stout on the first and disappear on the tenth. All have the spines short and 

 weak. On the second is a displaced rib head which might be mistaken for a chevron, 

 but in common with the other members of the order the first few caudals ha\e simple 

 intercentra and the chevrons begin more posteriorly. 



Between the sixth and seventh the first chevron appears. It is represented by 

 the proximal end only, but it shows the presence of a long distal process divided 

 proximally by an elongate foramen as in Dimetrodon, No. ii2 University of Chicago 

 (plate 21, fig. 9). The lower edges of the articular faces of the centra are cut away 

 to accommodate the wedge-like head of the intercentrum. By the thirteenth or four- 

 teenth caudal the vertebrse have become slender and elongate. The bottom line is 

 smooth, not marked with longitudinal lines as in some of the specimens from Illinois. 

 Chevrons are still present. Isolated vertebra show the tail to have been continued to 

 very slender proportions. 



Shoulder girdle: The imperfect scapula of both sides are preserved seemingly 

 in natural position and possibly inclosing and hiding some of the anterior vertebrae. 

 The scapula of the left side is preserved from the distal end to the center of the artic- 

 ular face, that of the right side from the distal end nearly to the articular face. The 

 form is in general the same as Dimetrodon. The shaft is curv-ed and is penetrated by 

 a foramen just distal to the articular face ; another foramen penetrates the bone just on 

 the scapular edge of the articular face. The articular face is deep, but is straighter 

 than in Dimetrodon in correlation with the simpler head of the humerus. The prox- 

 imal end of a scapula in the Chicago collection, No. 6540, probably belongs to this 

 species. On the anterior (dorsal) edge of both scapulae near the middle are fragments, 

 which are evidently the distal ends of the clavicles. On the right scapula a thin 

 splint of bone lies on the edge of the scapula and on the fragmentar>- end of the 

 clavicle. This is in exactly the position of a cleithrum. In some of the scapulae of 



