352 



The last specimen which I have now to notice was obtained by F. Nicholson, Esq., 

 from the same freshwater deposits at Clifton Plains, Darling Downs, Queensland. I am 

 indebted to the kindness of Professor Harkness, of Queen's College, Cork, for the oppor- 

 tunity of here describing and figuring it. It either exemplifies the largest observed 

 variety of Phascolomys gigas, or indicates a still larger species, i. e. one in which modifi- 

 cations of the shape of the jaw may be associated with its superiority of size. Of this 

 the mutilated state of the fragment does not permit me to judge, and I am disposed to 

 refer the specimen to a large old male of Phascolomys gigas. 



The longitudinal extent of the outlets of the last three molars of Mr. Nicholson's fossil 

 (Plate LXIII. fig. 4, m 1,2,3) is 3 inches 1 line; they show the same kind and degree 

 of decrease of size; from the first to the third as in the smaller examples of the species. 

 The breadth and apparent depth of the ectalveolar groove (ib. figs. 3 & 4, u) are as in 

 the first-described mandible (Plates LXI. & LXIL). The fore part of the base of the 

 coronoid or ascending ramus (ib. fig. 3, q) and of the ectocrotaphyte ridge (ib. h) show 

 likewise the same relative positions. On the inner fractured side of this specimen the 

 large inner division of the dental canal is seen about 9 lines above the closed ends of the 

 last two alveoli. 



§ 4. Conclusion. — In the case of Phascolomys, as of most Mammalian genera, when 

 due time and pains are applied to the acquisition and study of the fossil evidences, the 

 number of species which have passed away is found to exceed that of the living ones 

 which remain. 



Until comparatively lately the Wombat was known to zoologists as a solitary excep- 

 tional form of small Tasmanian marsupial, peculiar in its scalpriform dentition com- 

 bined with burrowing habits*. We now know this generic form under many specific 

 structural modifications, and with gradations of bulk rising from that of a Marmot to 

 that of a Tapir. 



The rodent type of incisors, both as to number and kind, are retained in all, certainly 

 in the lower jaw of the gigantic species; but it would not be safe to infer that the 

 subjects of the present Paper burrowed like the smaller living Wombats. 



If we knew the Hare [Lepus Umidus) only by fossil remains, we should err in attri- 

 buting to it the habits and mode of life of the smaller species, Lepus funiculus. It is 

 probable that the larger extinct Wombats did not conceal themselves under ground. 



What we know is, that of the series of forms specifically varying the generic type of 

 Phascolomys the larger ones have perished. Here, as in the case of the gigantic 

 wingless birds of New Zealand, size and bulk seem to have been a disadvantage in the 

 " contest for existence "*f\ The small burrowing KivisJ, like the small Wombats, have 

 sirvived. Phascolomys gigas and Phascolomys magnus are not likely to have escaped 

 observation if they still lingered in any of the localities made known by the adventurous 



* Hence the synonym, Phascolomys fossor, of "Wagner. 



+ Owen, " On Dinornis," Tart IV., Trans. Zool. Soc. vol. iv. (1850) p. 15. 



X A^tertjx ceustralis, Shaw Apteryx Owenii, Gould. 



