180 dr. r. broom ox the structure and [June 4, 



more feeble, and the claws have been only about one-third the 

 size of those in the manus. 



" Platypodosaurus robustus, Owen." 



In 1860 and 1881 Owen (8, 9) described in two papers parts of 

 the skeleton of a large Anomodont reptile to which he gave the 

 name of Platypodosaurus robustus. The remains comprised a 

 number of vertebra?, a scapula, a humerus, the sternum, the greater 

 part of the pelvis with the sacrum, a portion of one femur, and 

 some phalanges. Unfortunately the head was missing. Owen 

 recognized a number of affinities between the bones and those of 

 Dicynodon, but was chiefly impressed by the many Mammal-like 

 characters displayed, and particularly by the striking resemblances 

 many of the bones showed to those corresponding in the Mono- 

 tremes ; and he suggests that the Monotremes may be the de- 

 scendants of reptiles closely resembling Platypodosaurus. 



Lydekker (7), in the ' British Museum Catalogue of Fossil 

 Reptiles,' places Platypodosaurus among the Dicynodontia as a 

 doubtful species, and expresses his opinion that from the general 

 Dicynodont character of the specimens, the remains " are referable 

 either to Udenodon or Eudothiodon " 



As nothing has hitherto been known for certain of any of the 

 bones of either Udenodon or Eudothiodon except the skull, no 

 advance beyond Lydekker's position has been possible. Now, 

 however, that the limb-bones of at least two species of Udenodon 

 are known, it is possible to come nearer a solution of the Platypo- 

 1 1 'i ost i ur a ^-problem. 



The chief distinctive features of the Platypodosaurus specimens 

 are the great development in the humerus of the delto-pectoral 

 crest which forms a downward projection, and the presence of a 

 marked tricipital prominence. In Udenodon gracilis both of these 

 characters are found, and the general proportions of the humerus 

 are strikingly similar to those in Platypodosaurus. The sternum 

 of Platypodosaurus does not differ greatly from that of Udenodon 

 baini. The scapula agrees so closely with that of U. baini that 

 bad that of the latter been found alone it Mould almost certainly 

 have been referred to a young specimen of Platypodosaurus. 

 The femur of Platypodosaurus, so far as is known, differs somewhat 

 from that of U. gracilis, especially in the greater development 

 of the great trochanter, and in the less development of the small 

 trochanter; but it agrees closely with the femur of U. baini. 

 The pelvis of the larger anomodont, so far as it is preserved, 

 agrees very closely with that of U. gracilis in its general 

 proportions, and, if allowance be made for imperfections, probably 

 also in its contours. The vertebrae differ very considerably 

 from those of U. baini which I have figured. This is probably 

 due to their belonging to different regions of the column in the 

 two species. 



From the close agreement between the bones of Platypodosaurus 

 and those of Udenodon gracilis and U. baini, there seems to be 



