MAMMALIA. 315 



The MONODELPHIA, comprehend the great majority of 

 the mammalia. In this group the young have attained, at 

 birth, their full development, and require only the care of the 

 mother and the nourishment of her milk ; they have neither 

 a marsupium nor marsupial bones. 



MAMMALIA DIDELPHIA 



Have an organisation inferior to that of the monodel- 

 phians : their brain, dental system, and skeleton, aiford 

 proofs of an organic inferiority. If the few facts we possess 

 relative to the jaws found in the Stonesfield slate at the 

 base of the great oolite are confirmed by subsequent ob- 

 servers, then the creation of this sub-class must have long 

 preceded that of the higher mammals. The Stonesfield fos- 

 sils have been referred by Professor Grant of London, and 

 the late Professor De Blainville of Paris, to reptiles ; and 

 by MM. Valenciennes and Dumeril in France, and Professor 

 Owen of London, to mammifera.* The anatomical evidence 

 is in favour of the latter opinion. 



These jaws are referred to two genera, Thylacotherium, 

 which has numerous smal^ bifanged molar teeth, of which the 

 annexed wood-cut will convey a good idea. Two species of 

 this genus have been found at Stonesfield. 



FIG. 216. Jaw of the Thylacotherium from Stonesfield. 



* Mr. "Waterhouse, of the British Museum, whose profound knowledge of 

 the Mammalia entitles his opinion to the highest consideration, has no doubt 

 as to the Mammalian character of these jaws. The specimens which he 

 kindly showed us, exhibit the mammalian characters in a marked degree. 



