394 MARSUPIALS. 



pulps, but are, especially in the lower jaw, shorter and less curved 

 than in the placental Glires ; they present a subtriedral figure, and 

 are traversed by a shallow groove on their mesial surfaces. 



The spurious molars present no trace of that compressed struc- 

 ture which characterizes them in the Koala and Kangaroos, but have 

 a wide oval transverse section ; those of the upper jaw being tra- 

 versed on the inner side with a slight longitudinal groove. The true 

 molars are double the size of the premolars : the superior ones are 

 also traversed by an internal longitudinal groove, but this is so deep 

 and wide that it divides the whole tooth into two prismatic portions, 

 with one of the angles directed inwards. The inferior molars are in 

 like manner divided into two triedral portions, but the intervening 

 groove is here external, and one of the facets of each prism is turned 

 inwards. All the grinders are curved, and describe about a quarter 

 of a circle : in the upper jaw the concavity of the curve is directed 

 outwards ; in the lower jaw, inwards. The false and the true 

 molars like the incisors, have persistent pulps, and are consequently 

 devoid of true fangs, in which respect the Wombat differs from all 

 other Marsupials, and resembles the extinct Toxodon, the dentigerous 

 Bruta, and many of the herbivorous Rodentia. The incisors and the 

 first molar tooth are shed when the animal is young ; the latter is 

 superseded by the premolar tooth and the four true molar teeth 

 succeed each other from before backwards. 



In all the placental Rodents, which have more than three molars 

 in each lateral series, the additional ones are placed at the anterior 

 part of the row, and are subject to displacement by a permanent 

 successor in the vertical direction, and consequently are essentially 

 "premolars," or spurious molars; the Wombat strikingly manifests 

 its marsupial character in having four true molars on each side of 

 both jaws. 



155. Diprotodon. — The ossiferous caves and the superficial allu- 

 vial or pleistocene deposits of Australia have yielded evidences 

 of still more gigantic and extraordinary forms of the Marsupialia 

 than the Titanic Kangaroos. Amongst the fossils from WeUington 

 valley, first brought to England by Sir Thomas, then Major Mitchell, 

 I recognised in a large incisive tusk such marks of similarity to 



