350: PEOCEEDIJSTGS OF THE aEOLOGICAL SOCIETY. [June 4, 



for vegetable food ; and the position of the condyle, the slenderness 

 of the coronoid, and other characters of the lower jaw are in con- 

 formity to that regimen. In Thylacoleo the lower canine or canine - 

 shaped incisor projected from the fore part of the jaw, close to the 

 symphysis, and the corresponding tooth in Plagiaulax more closely 

 resembles it in shape and direction than it does the procumbent in- 

 cisor of Hypsiprymnus. Prom this genus Plagiaulaoo differs by the 

 obliquity of the grooves on its premolars ; by having only two true 

 molars in each ramus of the jaw, instead of four ; by the salient angle 

 which the surfaces of the molar and premolar teeth form, instead of 

 presenting a uniform level line ; by the broader, higher, and more 

 vertical coronoid ; and by the very low position of the articular 

 condyle. 



"^ The physiological deductions from the above-described charac- 

 teristics of the lower jaw and teeth of Plagiaulaoo are, that it was a 

 carnivorous Marsupial. It probably found its prey in the contem- 

 porary small insectivorous Mammals and Lizards, supposing no her- 

 bivorous 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 correlations, that Pla- 

 giaulaoG 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 AmpMtherium. The question 

 then was, whether the fossil was mammal or reptile ; and the foun- 

 dations 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 Mam- 

 malia — the teeth and correlated organs — so unstable or so obscure, 

 that of two palaeontologists, the same dental and mandibular mate- 

 rials 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 fol- 

 lowed by the observers in dealing with the evidence ? 



As the Geological Society gave to my original communication 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 description 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 * Palseontology' professes 



* Palasontology, p. 353. I entertain strong doubts about the soundness of the 

 deduction which makes Stereognaihus to have been herbivorous. 



