

ITS DISPUTED AFFINITY. 483 



Lizards, supposing no herbivorous form, like Stereognathus, 

 to have co-existed during the Upper Oolitic period.' ' 



We have here an opinion, professing to be founded on the 

 high ground of a connected series of physiological correla- 

 tions, that Plagiaulax was a carnivorous Marsupial ; while 

 the same materials led me to infer that it was phytophagous. 

 These diametrically opposed inferences recall, in some degree, 

 the discussion, famous in its day, respecting the disputed 

 affinities of Amphitherium. The question then was, whether 

 the fossil was mammal or reptile ; and the foundations of 

 Palaeontology were supposed to be concerned in the issue. 

 In the present instance the area of the field of difference is 

 less, but the interests involved are still important. Are the 

 indications of palaeontology, more especially in its great 

 stronghold in the Mammalia — the teeth and correlated or- 

 gans — so unstable or so obscure, that of two palaeontolo- 

 gists, the same dental and mandibular materials shall lead 

 the one to infer that the fossil form was a vegetable feeder, 

 and the other that it was a predaceous carnivore ? Or does 

 this conflict of opinion arise from different methods having 

 been followed by the observers in dealing with the evidence ? 



As the Geological Society gave to my original communi- 

 cation a place in its Journal, I feel bound, in the interest of 

 science, either to support the opinion which I then advanced, 

 or frankly to admit the correction, if I am found to be in 

 error. I am further impelled by my sense of self-respect, as 

 an observer, to consider whether — apart from the conclusions 

 — I have fallen into such errors of observation and descrip- 

 tion as would necessarily be implied, should Professor Owen's 

 manner of viewing the objects prove correct ; and if so, to 

 explain the fallacious train of reasoning which led me astray ; 

 for I cannot plead the excuse that the account was written 

 in haste, or without due consideration. 



If the data, upon which the author of ' Palaeontology ' 

 professes to rest his physiological deductions, were sound, 

 the demonstration would be complete. They are put together 

 with an exemplary show of harmony, and, with a single ex- 

 ception, every link in the chain is supplied. But there are, 

 in the case, considerations of paramount import in an argu- 

 ment of this nature, that lead me to question their soundness, 

 and to dissent from the conclusions. 



And first, as regards the admitted facts. Professor Owen 

 agrees that the Purbeck remains establish two species of 

 Plagiaulax ; and as he has adopted two of the woodcuts 

 given in my original description of these species, it is pre- 



1 Palaeontology, p. 353. I entertain I the deduction which makes Stcrcogna- 

 stronc; doubts about the soundness of thus to have been herbivorous. 





VOL. II. F P 



