PROGRESS IN VERTEBRATE PALEONTOLOGY 451 



almost the only point on which most authorities are agreed being 

 that creodonts include the ancestors of the modern Carnivora. 

 Much depends on the interpretation of the dental formula of the 

 carnivorous marsupials — that is to say, whether it corresponds (as 

 the writer believes it does) with that of creodonts, or whether it 

 is altogether different. That the creodonts are a very primitive 

 group (possibly the direct descendants of anomodont reptiles) 

 seems to the writer almost certain. That they are also in some 

 way related to the sparassodonts likewise appears to him most 

 probable. On the other hand, it is difficult to believe that there 

 is not some affinity between sparassodonts and marsupials, 

 although the writer cannot now (as he once did) definitely 

 support the view that the two should be referred to the same 

 division. 



To revert for a moment to Mr. Sinclair's memoir, it should 

 be added that it contains much valuable information with 

 regard to the undoubted marsupials of the Patagonian 

 Tertiaries. 



Another American memoir of considerable interest, of which 

 copies reached this country in November, 1905, is one by Mr. 

 Earl Douglass on Tertiary Mammals from Montana, published 

 in the Memoirs of the Carnegie Museum, Pittsburgh. In addition 

 to the remains of a number of creodonts, more especially of 

 the genus Ictops, a small skull is described under the name of 

 Xenotherium unicum and provisionally referred to the Mono- 

 tremata. If trustworthy, such an identification would be of the 

 highest interest ; but the question is whether the evidence is 

 sufficient even to justify the provisional reference. In both 

 groups of existing monotremes the skull is of an extremely 

 specialised type, and in the adult at any rate edentulous ; and 

 this being so, it seems almost essential to know the nature of 

 the shoulder-girdle before referring a toothed species (unless 

 the teeth recall the deciduous dentition of Ornithorhynchus) 

 to the order. 



Continuing our brief survey of American work, the next on 

 the list is a paper by Messrs. Matthew and Gidley on the fossil 

 Equidce of the Dakota Miocene. The paper is, however, merely 

 a preliminary one, dealing with the description of new speci- 

 mens ; but the results obtained during their study are deemed 

 of such importance as to justify a future memoir in which all 

 the species of Miocene three-toed horses will undergo revision. 



