104 



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 per- 

 form the duties required of a predaceous carnivore. 



" Magnitude in this ease is an important ingredient, as it necessarily involves measure 

 of force. Could P. minor have preyed on small Mammals and Lizards? Is it not 

 more probable that this pigmy form was itself an object of prey in the Purbcck 

 Fauna?"i 



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

 'Quarterly Journal of the Geological Society of London' for August, 1S57 (vol. xiii, p. 281)," 

 reproduced in the subsequent polemical paper of Dr. Falconer, in ' Quarterly Journal,' &c, 

 for June, 1SG2 (vol. xviii, p. 367), and copied in pi. 34, fig. 2, of the Posthumous Work 

 ' Palaeontological Memoirs' (p. 41G), shows two molars and four premolars; the incisor is 

 neither chisel-shaped nor procumbent ; but rises with a slight curve to its 

 Pig. 21. pointed apex at an angle of 120° with the line of the molar alveoli (fig. 21). 

 (J^^tor^ 7 The length of the dental series from the apex of the laniariform incisor to 

 Mandible and teeth * ne mn( ^ P ar ' °^ sccon( l molar is seven sixteenths of an inch, precisely the 

 nat. size, piagiau- ] ell orth of the dental series in Urofrichvs tatpo'ides — a transitional Shrew five 



la.v minor. o i 



inches long, from the snout to the tip of the tail, with a skull one inch in 

 length, and a pair of lower pointed incisors (fig. 17) upcurved at the same angle as in 

 PI. minor, but relatively less and shorter (fig. 22, a). 



I am not cognizant of any grounds afforded by Zoology which forbid the supposition 

 that a Mammal of five inches in length, with the carnivorous type of dentition of 

 Plagiavlax, may have been able to capture and kill the diminutive species of Lizard 

 {Saurillus,- &c.) abundantly associated with Plagiavlax in the Purbcck shales. Com- 

 parative anatomy suggests that the modifications of the dentition of Plagiavlax minor, as 

 compared with the similarly sized Shrew {Urotrichus), would give the Purbeck Marsupial 

 both the disposition and power to attack and prey upon animals of a larger size and 

 higher organization than worms and insects. But the question of the carnivority of 

 the genus Plagiavlax, if weighed by ' magnitude as a measure of force,' is not fully or 

 fairly tested by the exclusive example of the most diminutive species. 



In Plagiavlax Falconeri (PI. IV, fig. 16) -the extent of the dental series, lower jaw, is 

 nine sixteenths of an inch: in Plagiavlax Becklcsii (ib., figs. 10, 11, 12, and fig. 8, p. 86), 

 it is ten sixteenths of an inch. 



The entire length of the mandible in this species, inclusive of the incisor, in a straight 

 line, is one inch three sixteenths ; the depth of the ramus at the back part of the large 

 carnassial is five sixteenths of an inch. 



In the Weasel (Mtisfela vulgaris, fig. 22, c) the extent of the dental series, lower 

 jaw, is eight sixteenths of an inch ; the entire length of the mandible, inclusive of the 



' Falconer, op. cit. lb., p. 363 ; ib., p. 448. 



2 Owen, ' Quarterly Journal of the Geological Society,' No. 40, 1854, p. 420. 



