112 



REVISION OF THE PELYCOSAURIA, 



the transverse process has greatly shortened in the posterior dorsals and lumbars, and 

 its terminal face is now nearly on a level with that for the head of the rib, the two 

 faces approach each other as the capitnlum and tuberculuni of the rib grow closer 

 together nntil they unite. (See figs. 51-53-) 



The shoulder girdle is described largely from that of specimen No. 114 Univer- 

 sity of Chicago, D. dolloviaiius, which closely resembles that of D. inciswiis, but is more 

 perfectly preserved. Scapula, coracoid, procoracoid, clavicle, interclavicle, and proba- 

 bly a rudimentary cleithrum are present. 



Fig. 40.— Diagram of shoulder girdle ot D. 

 dollooianus. No. 1 1 4 University of Chi- 

 cago. < /, clavicle ; pco, procoracoid ; 

 fo, coracoid; s</>, scapula; c//, cleith- 

 rum. 



Fig. 41. — Inner surface of scapula ot D. incisi- 

 cus. No. 4 1 3 1 Am. Mus. sr/, scapula ; 

 CO, coracoid ; /;r, procoracoid. X /4. 



The scapula is elongate with an ex- 

 panded distal end and narrow shaft; the 

 proximal end widens, the anterior portion 

 is thin and unites finnly with the procora- 

 coid, though the suture remains traceable 

 through life. On the posterior edge the 

 bone is very heavy and fonns the upper 

 half of the deep cotylus. Just above the 

 cotylus a foramen penetrates the bone and 

 opens into a deep semilunar cavity on the 

 inner side (fig. 41); just in front of the 

 cotylus a foramen penetrates between the 

 scapula and procoracoid and opens into the 

 same cavity on the inner side. This is the 

 homologue of the coracoid foramen of other 



forms. 



The procoracoid terminates anteriorly in a thin, straight edge, which shows signs 

 of having borne a heavy epicoracoidal cartilage. 



The coracoid is a small bone, but it is very strong and forms the lower half of 

 the humeral cotylus. The coracoidal portion of the cotylus is set at an angle to the 

 scapular portion .so that the whole face is twisted to accommodate the oblique articu- 

 lar face on the head of the humerus. 



The cleithrum is doubtful, but a small Ijone in the Clepsydrops natalis can only 

 be interpreted as this element and some specimens of Dimeirodon show an indefinite 



