2l6 THE AFFINITIES OF TOXODONS chap. 



There is no doubt about the close alliance of the two genera 

 just referred to. It is more doubtful whether Homalodonto- 

 therium and its allies should be placed, as they often are, in the 

 neighbourhood of the Toxodonts. Horiialodontothervmn owes its 

 name to its even row of teeth without a diastema. It was a 

 creature of equally large size with Toxodon, and also came from 

 the Tertiary strata of Patagonia. The teeth are the typical forty- 

 four, and the molars like those of a Ehinoceros ; they are, how- 

 ever, brachyodont and not hypselodont as in Toxodun. This genus, 

 however, shows an important difference from the Ehinocerotidae 

 and from the other Toxodontia in the fact that it was five- toed, and 

 that the bones of the carpus and tarsus are set in relation to each 

 other in the linear serial fashion. 



Undoubtedly a near relative of Homalodontotlhermm is Astrapo- 

 therium. This creatm-e was of equal bulk, and was also Patagonian 

 in range. The teeth are reduced in numljer, but the animal was 

 provided, like a Wild Boar, with great tusks, which were, however, 

 formed by the incisors. This animal is very imperfectly known ; 

 it is the form of the molars and the large size of the incisors which 

 have led to its association with the Toxodontia. As to the resem- 

 blance of the teetli of this genus and of Homalodontotheriuni to 

 those of Rhinoceros, it is difficult to regard it as evidence of near 

 affinity. The likeness is probably to be looked upon as a case of 

 parallelism in development. Exactly the same explanation is 

 possibly to be given to the likeness which the teeth of Toxodon 

 and Nesodon show to Eodents, or even to Edentates. As to their 

 affinities Zittel observes : — 



" The entirety of their osteological characters argues for the 

 Toxodon a separate position in the neighbourhood of the Perisso- 

 dactyla, Proboscidea, Typotheria, and Hyracoidea. Tlie relations 

 to the liodentia rest mainly upon the converging development of 

 the teeth, not upon true relationship." 



SuR-OuDER 6. PEOBOSCIDEA. 



Large vegetable-feeding animals, usually scantily covered with 

 hair, and with the nostrils and upper lip drawn out into a long 

 proboscis. Digits five on l)oth limbs. Femur and humerus not 

 bent upon lower leg and fore-arm in a position of rest. Skull 



