630 PROF. H. G. SEELEY ON [Aug. I9OO, 



Affinities of the Shoulder-Girdle. 



The shoulder-girdle has its first affinities with the Anomodontia, 

 in the second place with the Monotremata, and in the third place 

 with Eryops. The first affinity with the Anomodontia, and the 

 second with the Monotremata, are of the same order. In wanting 

 the anchylosis of the precoracoid to the coracoid and scapula, 

 Aristodesmus differs from the Russian Deuterosauria, the Pareia- 

 sauria, and apparently the Theriodontia. 



The loose relation of the precoracoid to the coracoid is not 

 perhaps more marked in Echidna than in Keirognathus. In 

 Procolophon, although the union appears to be sutural, it is a 

 straight suture. 



Affinity with Procolophon is most evident in the forward extension 

 of the precoracoid, so that it has a lateral surface in advance 

 of the scapula. This character is a distinction from all other 

 Anomodonts, and supports the classification of Procolophon as a 

 primary division of the group, well distinguished from Pareiasauria. 



The Fore-Limb. (Fig-. 4, p. 631.) 



The bones of the fore-limb are only evidenced on the right side 

 of the body, though fortunately there are superior and inferior 

 impressions of the humerus, alna and radius, carpus, metacarpus, 

 and digits. In form, proportion, and many details of structure, the 

 limb somewhat resembles Echidna. These Monotreme characters 

 extend to the form of the humerus, the proportions of ulna and 

 radius, and the general aspect of the digits ; though the phalanges 

 are relatively longer, and the claw-phalanges relatively rather 

 smaller. Prof. AYiedersheim has drawn four digits in his restora- 

 tion of the fore-limb, and four only are preserved on each slab. 

 There appears to be evidence of five digits, by superimposing the 

 upper and lower surfaces. Five is also the number in the hind- 

 limb. One remarkable feature of the fore-limb is the way in which 

 the fifth digit is directed outward at right angles to the ulna; and 

 the outermost digit is directed forward below the radius, so that the 

 five digits radiate towards the outer side of the foot. 



(a) The Humerus. 



The ventral surface of the humerus shows the transverse 

 expansion, and concavity from side to side, of the proximal fan- 

 shaped half of the bone, which is in articular relation with the 

 coracoid and is relatively wider than in Echidna. This transverse 

 extension and the absence of an hemispherical head are shared 

 with Anomodonts. The proximal articular surface is narrow and 

 long, with downward reflexion of the radial part of the bone. 

 Its articular surface is markedly convex along its length : the 

 convexity consisting of two portions, which, though not sharply 

 defined, are inclined one to the other at rather more than a right 

 angle. 



