Yol. 56.] AKISTODESMUS KUTIMEYERI. 641 



The Armour. 



The dorsal surface of the animal appears to have carried two or 

 three longitudinal rows of irregular small scutes, which were 

 isolated one from the other. The rows were widely separated. 

 On the cast, between the impressions of the ribs, are a series of 

 holes, one between each pair of ribs as a rule. Their forms are 

 irregular, identified with uncertainty ; they may indicate prominent 

 dermal scutes. 



III. Conclusion. 



The skeleton now described appears to' leave no doubt as to its 

 systematic position. The skull and shoulder-girdle demonstrate 

 a preponderance of Anomodont characters. The Anomodontia in 

 the present state of knowledge are better denned by the structures of 

 those regions than in other parts of the skeleton. But while the 

 shoulder-girdle is distinctly Anomodont, the free condition of its 

 constituent bones makes a partial resemblance to the Monotremata. 

 The pelvis also is Anomodont, so far as can be judged from its state 

 of preservation. 



On the other hand, the limbs in Aristodesmus make a more 

 decided approximation to those of Monotreme mammals than has 

 hitherto been seen in any fossil, although they also show r affinity 

 with the Anomodontia. Judged by the limbs alone, the evidence 

 already available from this genus and African Anomodonts almost 

 obliterates the interval between Monotreme and reptile ; just as the 

 evidence drawn from comparisons of the skull alone, tends to keep 

 the two groups distinct. 



There is no proof at present that the skull may make a complete 

 transition between the two groups. Chelonian reptiles have shown 

 that the reptilian prefrontal bone may in most genera be combined 

 with the nasal bone, and yet remain distinct in a few types like 

 the fossil Mhinochel-ys and the existing Podocnemys. There is no 

 evidence that the union between the frontal and postfrontal bones, 

 or between the dentary bone and other elements of the mandible, 

 is obliterated in reptiles. So long as the lower jaw is composite, 

 and prefrontal and postfrontal bones exist, the animal may be 

 technically a reptile ; although the blending of the prefrontal and 

 nasal bones in Chelonians shows the first step in a change by which 

 the reptilian skull might lose its most distinctive characters. The 

 Chelonian modification rather tends towards the possibility of reduc- 

 tion of the reptilian to the mammalian type of skull, but lends 

 no support to a supposition that a mammal might preserve pre- 

 and post-frontal bones, a parietal foramen, or a composite lower 

 jaw. The obliteration of distinct ossifications varies in time of 

 disappearance. 



Until the embryology of Echidna is known, it would be pre- 

 mature to affirm that the Anomodontia and Monotreme mammalia 

 are not members of a natural alliance, which might be termed 

 Theropsida. From the point of view of the osteologist, it may 

 be a reasonable inference that the interval between the Monotreme 



