Vol. 56.] ARISTODESMUS RUXIMEYERI. 627 



staff of the interclavicle.' These bones are the precoracoid and 

 coracoid. Laterally, the two scapulas extended upward and backward 

 dorsally over the ribs. These bones form a strong pectoral girdle. 

 The head of the humerus is preserved in close contact with the 

 articular face of the coracoid. The bones of the shoulder-girdle are 

 situate far forward, just behind the animal's head, as in Pareiasaurus 

 and Proeolophon. The antero-posterior extent of the bones corre- 

 sponds to about four vertebras. In general character the shoulder- 

 girdle is Anomodont. Pareiasaurus and Mhopalodon have the 

 constituent bones anchylosed together, while this rather resembles 

 Proeolophon and Keirognathus. The former has a similar inter- 

 clavicle, but exhibits closer union between the precoracoid and 

 coracoid. The latter appears to have the precoracoid and coracoid 

 similarly free ; but its interclavicle is in form unlike the bone in 

 other Anomodonts. The resemblance to Eryops deserves attention, 

 though the shoulder-girdle bones are united in that Labyrinthodont. 



(a) The Interclavicle. 



There is a general correspondence of T-shaped form between this 

 bone and the interclavicle in Proeolophon and Pareiasaurus. The 

 chief difference in these types is in the parallelism of the sides of 

 the longitudinal staff of the bone in Proeolophon, and the posterior 

 divergence of the sides in Pareiasaurus, in which however the 

 extremity of the staff of the bone is imperfectly preserved. In this 

 Bunter fossil the interclavicle is intermediate in character between 

 those genera, for there is a very slight posterior widening of the 

 staff, and it is so short as not to extend back beyond the middle of 

 the coracoids. 



The indications preserved on the right side give a transverse 

 width to the bar, so that it is actually longer than the staff. In 

 Proeolophon the staff is much longer than the transverse bar. In 

 Aristoclesmus the bono is relatively rather small, since the transverse 

 bar, which is inclined a little backward, does not extend laterally 

 outward so far as does the precoracoid. ' This character may not be 

 of much importance, since in Keirognathus the lateral arms of the 

 interclavicle are very short, and the clavicles rest upon the anterior 

 margins of the precoracoid bones. In Pareiasaurus, on the other 

 hand, the lateral arms of the interclavicle extend outward beyond 

 the precoracoids, so as to completely separate those bones from 

 the clavicles, which are carried in front of the interclavicle upon 

 the transverse bars. The widening of the staff of the interclavicle, 

 at its hinder extremity, exceeds *4 inch. In its middle length the 

 width is *3 inch ; and it widens again anteriorly towards the trans- 

 verse extension of the anterior bar. These lateral arms measure 

 from front to back at their origin about *3 inch, and "1 inch each 

 at the outer extremity. 



The external surface of the interclavicle is elevated. This makes 

 a flat median longitudinal surface, on each side of which the staff 

 is slightly grooved. The grooving is not distinct at the posterior 



