PURBECK FORMATIONS. 



105 



Fig. 22. 



Mandible and teeth ; 

 A, Urotrichus talpo'ldes ; 

 B, Didelphys dursi- 

 gera ; C, Mustela vul- 

 garis ; nat. size. 



Fig. 23. 



incisors, in a straight line, is thirteen sixteenths of an inch ; the depth of the ramus at 

 the back part of the large carnassial is two sixteenths of an inch. 



In the Opossum, Didelphys dorsigera (fig. 22, b), the extent of the mandibular dentition 

 is ten sixteenths of an inch. 



With the greater relative depth and consequent strength of the 

 jaw of Plagiaulax (fig. 23), a greater size and strength of both 

 laniary (^) and carnassial teeth (/j) are concomitant. The condyle {b), 

 which is on the level of the dental series in the Weasel, and above it 

 in the Opossum, is below that level in Plagiaulax. Every modifica- 

 tion of the small Marsupial by which it departs from the little blood- 

 thirsty placental is in the direction of greater carnivority. 



In Phascogale penicillata the extent of the dental series, lower 

 jaw, is fourteen sixteenths of an inch. It has four true molar teeth, 

 relatively smaller laniaries, and still smaller sectorial premolars ; the 

 mandibular condyle is raised a little above the dental line ; the 

 carnivorous adaptation of both jaw and teeth is less marked than 

 in the Purbeck Marsupial. But what is the testimony in regard 

 to the habits of the existing pouched carnivore no bigger than 

 a rat? 



Gould, who would be the last to repeat testimony to which *( 

 zoology and comparative anatomy ran counter, writes : — " Phascogale 

 penicillata, small as it is comparatively, is charged with killing fowls 

 and other birds." ^ I can bear personal testimony, and that to my 

 own loss, of the attack and slaughter of nearly full-grown Shang-hai 

 pullets by Mus decumanus. Comparative anatomy lends 

 more aid to the credibility of the predatorial power of the 

 carnivorous Marsupial than of the equally small Rodent ; 

 but that both of them do attack and destroy animals more 

 than twice their own size and weight is a zoological 

 fact. 



Though magnitude may be, in one sense, a measure of 

 force, it by no means necessarily involves, or teaches, the application of such force, and 

 consequently is anything but ' an important ingredient ' in the question of the carnivority 

 of Mus, Mustela, Phascogale, and Plagiaidax. 



But whatever bears on the interpretation of the singular dentition of the small 

 ' paucidentate ' Marsupial logically applies to the larger one. There I admit the 

 superiority of Mr. Krefft, Prof. Elowek and Mr. Boyd Dawkins, over Dr. Falconee, at 

 least in consistency. 



Mr. Krefft gives drawings of sections of the " lower incisor of Thylacoleo, Nototherium, 

 1 ' Mammals of Australia,' folio, Introduction, p. 18. 



14 



Mandible and teeth, 



Plagiaulax Becklesii ; 



nat. size. 



Fig. 24. 





Mandible and teeth with upper laniary 

 incisor, Potamogale velox ; nat. size. 



