184 Miscellaneous. 



The fossil is referred to a new genus — Aristodesmus. It is iden- 

 tified as an Anomodont reptile chiefly on the basis of resemblances to 

 Procolophon and Pareiasaurus. It is shown not to be a mammal by 

 the large parietal foramen, the composite structure of the lower jaw, 

 and presence of the prefrontal bone. It, however, differs from 

 known Anomodonts in making a somewhat closer approximation to 

 Monotreme mammals than has hitherto been evident, and this 

 correspondence extends to successive segments of both the fore and 

 hind limbs. 



The teeth are in sockets placed obliquely, with conical crowns 

 compressed to sharp lateral margins, and curved inward. The 

 proportions of the vertebral column are those of Echidna, though the 

 transverse processes are longer, as in Pareiasaurus. The ribs are 

 like those of a Monotreme, though the sacral ribs are longer. The 

 shoulder-girdle resembles that of Procolophon, and differs from all 

 other Anomodonts in the constituent bones being uuanchylosed, and 

 in the precoracoid having a large anterior extension in advance of 

 the scapula. The sternum appears to have been unossified, as in 

 Crocodilia. The humerus is widely expanded at both extremities 

 and twisted, but does not show the peculiar lateral curvature seen 

 in Monotremes. The ulna gives no evidence of an olecranon process ; 

 it is larger than the radius, and appears to articulate with the 

 humerus. The pelvic bones are without acetabular or obturator 

 perforations, are not anchylosed together, and the ilium is not ex- 

 panded transversely. The hind limb is no longer than tho fore 

 limb. The femur is more slender than the bone in Echidna. The 

 fibula is prolonged proximally beyond the stout tibia, round which 

 it may rotate. The proximal row of the tarsus is one large bone, 

 formed of the blended astragalus and os calcis. 



In conclusion, the author argues that the points of structure are 

 so few in which Monotreme mammals make a closer approximation 

 to the higher mammals than is seen in this fossil and other Anomo- 

 dontia, that the Monotreme resemblances to fossil reptiles become 

 increased in importance. He believes that a group Theropsida might 

 be made to include Monotremata and Anomodontia, the principal 

 differences (other than those of the skull) being that Monotremes 

 preserve the marsupial bones, the atlas vertebra, and certain cranial 

 sutures. Ornithorhynchus shows prefrontal and postfrontal bones, 

 and has the malar arch formed as in Anomodonts. 



Aristodesmus, which suggests this link, is at present placed in the 

 Procolophonia, a group separated from its recent association with 

 Pareiasaurus, and restored to its original independence because it 

 has two occipital condyles, with the occipital plate vertical, and 

 without lateral vacuities, and has the shoulder-girdle distinct from 

 Pareiasauria in the separate precoracoid extending in advance of the 

 scapula. — From the Proceedings of the Royal Society. (Communi 

 cated by the Author.) 





