ON THE SHOULl>ISR-GIRDLE AND EXTREMITIES OF ERYOPS. 363 



backwards, in the foi-m of a band, and it does not extend so far on the scapula as is 

 usual with Keptilia, and teiminatcs in a rather abrupt flat apex. The inferior 

 portion becomes horizontal and is directed forwards at an open an<^le, meeting its fel- 

 low on the middle line. This portion expands a little, presenting a thin edge poste- 

 riorly, and an oblique truncation inwards and forwards with grooved and finely 

 digitate edge, at the distal ind. The clavicles underlap the episternum. The latter 

 is a flat discoidal bone rather wider tiian long, with a regularly convex, thin posterior 

 edge. The lateral jjortions are overlapped by the prrecoracoids. The anterior border 

 is coai'sely toothed, as though for the attachment of an omosternum. Of true 

 sternum I do not observe any trace of sternum. 



The ditterences between the shoulder-giidles of Eryops and of Actinodon 

 (Gaudry) are considerable. The latter has been described and Hgui'cd ])y Professor 

 Gaudry, and I have had, through his kindness, the opportunity of examining the 

 typical specimen. An obvious diil'erence is that the latter genus, as in many Stego- 

 cephali, has the epistei'num and proximal parts of the clavicles sculptured on the 

 inferior (external) face, with exostosis, which occupies the true skin. The clavicle 

 articulates externally with a slender bone, which is regarded by Gaudiy as clavicle. 

 It occupies the position of the anterior thickened portion of the scapula in Eryops. 

 What its true homology is is not clear to me, but it is in the position of the epicla- 

 vicle of the fishes. The scapula is co'issified Avith the pra?coracoid. The true coia- 

 coid is very small, less even than in Eryo])s. An easily observed peculiarity of 

 Actinodon is that the episternum is longitudinal diamond-shaped, as in Stegoccphali 

 gem rally. 



The shoulder-girdle of Cricotus is in my collection, but is so diflicult to extri- 

 cate from the matrix that its chai'acters are not all clear. The clavicles are expanded 

 inwards over the edges of the episternum as in Actinodon, and more widely than in 

 Eryops, and the expanded surface is sculptured as in that genus. The slender part 

 of the clavicle is strongly curved upwards, as in Actinodon. The episternum is also 

 produced posteriorly as in Actinodon. 



As compared with the Pelycosaurian reptiles, the shoulder-girdle of Eryops and 

 its allies shows several im[)ortant points of resemblance, some of which I have already 

 described. iSuch are the small coracoid and large pra-coracoid, both coissilied with 

 the scapula in adults. The episternum in Dimetrodon at least, diiVers in its long nar- 

 row posterior pi-olongation, as in Lacertilia.'' The clavicles have not been described 

 in Clepsydropidie, although they have been in Diadcctidaj.f In the latter the clavi- 



•TraDsactions Amer. Phil. Soc, 188C, p. 292, PI. Ill, fig. D, where I inadvertenlly called it sternum. 

 tProc. Amer. Phil. Soc, 1883, p. 615. 



