Vol. 56.] ARISTODESMTTS RUTIMEYEET. 621 



slabs. Accordingly, in the following description I rely upon impres- 

 sions of bones, taken by myself from such parts of the skeleton as 

 would manifestly yield prints without the possibility of injury to the 

 matrix. 



These impressions suggest modifications of Prof, Wiedersheira's 

 osteological interpretations of the bones. What was regarded as 

 the humerus, I describe as the interclavicle. The scapula of 

 Wiedersheim's fig. 1 is the humerus ; the supra-scapula in his 

 fig. 2 is the left coracoid; but in fig. 1 it is the right scapula. 

 The bones interpreted in 1878 as right and left coracoids are 

 the precoraeoid and coracoid of the right side of the shoulder- 

 girdle. The bones named clavicles are ribs. A row of teeth drawn 

 upon the palate in the restoration, is doubtfully indicated in the 

 specimen. In place of the four digits to the hand, I find indications 

 of five. These modifications of interpretation reopen the question of 

 the animal's organization. The only alternative supported by 

 evidence of structure is, whether the remains should be referred to a 

 Triassic mammal, or to an Anomodont reptile. Against a mammalian 

 interpretation is, firstly, the presence of a large parietal foramen; and 

 secondly, a composite structure of the lower jaw. There is also the 

 presence of prefrontal, aud perhaps postfrontal, bones in the skull, 

 though as the external surface has been chiselled away the evidence 

 on these points is not complete ; and at the close of this paper 

 evidence is adduced to show that those bones are found in Ornitho- 

 rhynchus, together with a reptilian structure of the malar arch. 



The Anomodont structure may be affirmed, firstly, on a general 

 resemblance of the skull to the skull in Procolophon ; secondly, there 

 is absolute correspondence of the shoulder-girdle with that region in 

 Anomodont types, and a close approximation to Procolophon ; thirdly, 

 the great transverse expansion of the proximal and distal ends of the 

 humerus, which, like the shoulder-girdle, is only paralleled in 

 Anomodonts and Monotremes ; fourthly, a general correspondence 

 of the vertebras in plan, and especially in the articulation of the 

 ribs, with Pareiasaurus and Echidna-, fifthly, the Anomodont form 

 of the pelvis, without an obturator-foramen between the ischium 

 and pubis, or a perforation in the acetabulum ; sixthly, the close paral- 

 lelism in form of the femur to Echidna ; seventhly, the general 

 resemblance of the tibia and fibula to those of Pareiasaurus ; and, 

 eighthly, the structure of the tarsus, where the proximal row 

 consists of a single bone formed from the anchylosed astragalus and 

 os calcis. 



The most distinct approximations to Procolophon are the im- 

 anchylosed condition of the bones of the shoulder-girdle and pelvis ; 

 and the form of the skull, and smooth condition of the skull-bones. 

 In so far as the fossil diverges from Procolophon and Pareiasaurus, 

 it approximates to Echidna, especially in the characters of the 

 limb-bones, such as the humerus, ulna, femur, fibula, and proximal 

 elements of the tarsus. 



As the genus is new, the fossil may be known as 

 Aristodesmus Rutimeyeri ("W ieder she.im). 



Q. J. G. S. No, 223. 2 t 



