ITS DISPUTED AFFINITY. 



431 



assurance, that further research and future discovery will 

 only confirm and extend them. If the conclusions are chal- 

 lenged, science is invariably benefited by the controversy. 

 Different modes of analysis and different trains of ideas are 

 brought into conflict ; and landmarks are established for the 

 warning and guidance of future observers. 



Among the mammalian forms brought to light through 

 Mr. Beckles's important researches in the Purbeck Beds, 

 there was one which struck me with especial interest. I 

 found in it a singular combination of characters : — The den- 

 tition modified by suppression to as great an extent as in 

 any existing form ; strong analogies, in some respects, with 

 known genera, while in others it diverged from them very 

 widely. Early in 1857 I communicated to the Geological 

 Society an account of the genus Plagiaulax, which appeared 

 in the 13th volume of the 'Quarterly Journal' (p. 261 '). 

 About the same time an abridged description of the form, 

 illustrated by figures, was brought out in the Supplement to 

 the 5th edition of Sir Charles Ly ell's ' Manual of Geology ' 

 (1857, p. 17). On both occasions I arrived at the conclusion 

 that ' Plagiaulax may be regarded in the natural system as a 

 Marsupial form of Rodent, 2 constituting a peculiar type of 

 the family to which Hypsiprymnus belongs,' although widely 

 distinct from that genus. 



The only comment impugning this determination that has 

 come under my notice, appeared in the Article ' Palseon- 

 tology,' by Professor Owen, in the 8th edition of the ' Ency- 

 clopaedia Britannica, 3 published in January, 1859, and subse- 

 quently reproduced as a separate work. 4 The two accounts 

 differ in some unimportant particulars. I here cite the later 

 in date, as presumably conveying the latest views of the 

 author. The following are extracts : — 



' Two specimens exemplified the shape and proportions of 

 the entire jaw of this species (Plagiaulax Becklesii). The 

 foremost tooth is a very large one, shaped like a canine, but 

 implanted by a thick root in the fore part of the jaw, like 

 the large lower incisor of a Shrew or Wombat. The three 

 anterior teeth in place have compressed trenchant crowns, 

 and rapidly augment in size from the first to the third. 



1 See antea, p. 408.— [Ed.] 



2 I leave the words as they originally 

 stood ; but my meaning would have 

 been more accurately conveyed by the 

 expression ' Rodent type of Marsupial,' 

 ■ — rodent being here used in the large 

 sense, having reference to the plan of 

 dentition, characterized by two collateral 

 incisors in the lower jaw, as typically 



shown in the placental series by the 

 Rodentia and Cheiromys ; and in the 

 Marsupialia, by Phascolomys, modified 

 in the Macropodidw and the Phalan- 

 gistidm by the opposition, in the iipper 

 jaw, of several incisors. (See Cuvier, 

 Oss. Eoss. 4th edit. torn. v. p. 3.) 



3 Vol. xvii. p. 161. 



4 Palaeontology, 2nd edit. p. 353. 



