177 



A still more generalized type of dentition is shown by the multiplication of slightly 

 differentiated teeth in the genera Amphitherium, Amphilestes, Spalacotherium, Peralestes, 

 Stylodon, &c, of the lower and upper oolites. One solitary form {Myrmecobius) alone 

 remains at the antipodes with minute and slightly differentiated teeth, hi number ex- 

 ceeding the type one in most modern Mammals, and recalling that in lower and wider 

 vertebrate groups. 



The two or three smaller but functional premolars in advance of the large lower car- 

 nassial in the mesozoic Plagiaulax are reduced to two or three more minute functionless 

 and speedily lost premolars in the neozoic Thylacoleo. 



This fact invalidates the averment of " the contradictory bearing of the dental system 

 of Plagiaulax upon the assumption that the earliest Mammals had the full complement 

 of teeth :" which averment Dr. Falconer reiterates and " calls special attention to," in X. 

 p. 365, XI. p. 451. For if, in place of assuming Plagiaulax to be the earliest mammal, 

 and, as such, with the full complement of teeth, or " the oldest well-ascertained herbi- 

 vorous mammal," it be viewed as no more than it is, viz. a geologically earlier form than 

 Thylacoleo with a dentition similarly modified for carnivority, the degree of difference 

 between the two members of the Paucidentata is affirmatory instead of contradictory, 

 in relation to the rule in question, rightly stated. 



Relation of Size to Carnivority. — One other argument against the predatory way of life 

 of the subject of the present and preceding Sections remains for notice, although its very 

 suggestion implies a sense of the insecurity of the grounds on which the herbivorous 

 habits and affinities of Plagiaulax and Thylacoleo have been advocated. 



They are affirmed to have been animals too small, too feeble, to have preyed upon 

 others, especially when much larger than themselves. 



Whoever has witnessed the well-known zoological phenomenon of the pertinacious 

 pursuit and fatal attack of a hare by the diminutive weasel would pause, however, be- 

 fore venturing on such grounds of objection. 



Dr. Falconer, selecting for his purpose the most diminutive of the species of Plagi- 

 aulax, affirms : " The entire length of the specimen, including the six molars and pre- 

 molars, together with the procumbent incisor (according to the metrical line e), does 

 not exceed *4 of an inch, of which the six cheek-teeth united make only about two 

 and a half lines ("25 inch). I ask any zoologist or comparative anatomist to look at it, 

 and say whether the dental apparatus of this extremely minute creature is competent 

 to perform the duties required of a predaceous carnivore. Magnitude in this case is an 

 important ingredient, as it necessarily involves measure of force. Could P. minor have 

 preyed on small Mammals and Lizards 1 Is it not more probable that this pigmy form 

 was itself an object of prey in the Purbeck fauna'?"* 



To this I reply, that I have now before me the original of fig. 15, Plagiaulax minor 

 of the Quarterly Journal of the Geological Society of London for August 1857, xiii. p. 281, 

 reproduced in the subsequent paper of Dr. Falconer in Quarterly Journal &c. for June 

 1862 (X. p. 367), and copied in pi. 34. fig. 2 of the posthumous work (XI. p. 416). 



* X. p. 363 ; XI. p. 448. 



