98 THE MAMMALIA. 



at a much later date that E. Owen l traced similar 

 animals back to the Trias formation. 



In the so-called Ehaetic beds, one of the sections 

 of the Trias, a few minute teeth were found which 

 probably belonged to an Insectivorous Marsupial ; 

 these teeth have given rise to the genus Microlestes. 

 Again, in the Lower Lias (of the Jura formation), 

 fragments of lower jaws have been found that must 

 be regarded as belonging to small Insectivorous 

 Marsupials. Phascolotherium is most frequently 

 mentioned. Similar remains are found in the strata 

 directly below the Chalk formations, and among 

 these we have Plagiaulax, very remarkable on 

 account of the reduction and specialisation of its 

 dentition. In Fig. 2 we have the lower jaw of PL 

 minor (A) in natural size. Hence it was an animal 

 of the size of a mouse. In the enlarged jaw of 

 another species (Fig. 2, B) the premolar (?), marked 

 by number 4, and followed by two molar-shaped 

 teeth, shows the very marked character of the 

 genus, which is less distinct on the preceding 

 teeth i.e. the deep diagonal grooves. 



Owen looks upon all these imperfect remains as 

 ' generalised forms,' whereas Huxley asks, what are 



1 Owen, ' Monography of the Fossil Mammalia of the Mesozoio 

 Formation ' (Palceontological Society, 1871). 



