290 ORDERS OF MAMMALIA. 



smaller vertebrate animals ; and the same holds good of all 

 the fossil forms. 



As regards their distribution in time, the Marsuinalia 

 probably constitute the oldest of the Mammalian orders. 

 Owing, however, to the detached and fragmentary condition 

 of almost all Mammalian remains — consisting in many cases 

 of the ramus of the lower jaw, or of separate teeth — it is 

 not possible to state this with absolute certainty. The 

 oldest known European Mammal is the Microlcstes antiquus 

 (lig. 602) of tlie Upper Trias, only a few teeth of which 

 have been as yet detected. The earliest horizon on which 

 Microlcstes occurs is in a " bone-bed " in the Keuper of 

 Wlirtemberg ; but it has also been detected in the higher 

 " Ehsetic " beds. Prof. Owen believes that the Hypsiprym- 

 nopsis of Mr Boyd Dawkins, from the Ehffitic marls of 

 Somersetshire, is also referable to Microlestcs. Upon the 

 whole, it is most probable that Microlcstes was Marsupial ; 

 and it appears to be most nearly related to the little insec- 

 tivorous 3Iyrmecohius or Banded Ant-eater of New South 

 Wales (fig. 600). 



Fig. (300. — MyrmecoMus fujiciatus. 



Nearly allied to Microlcstes is a small Mammal, a lower 

 jaw of which has been obtained from the Trias of North 

 America, and which has been described under the name of 

 Dromathcrium sylvcstrc. This little animal (fig. 601) ap- 

 pears also to be Marsupial, and to be most nearly related 



