9 



canal is complicated by a moderately long and large caecum ; and, 

 while in the Sarcophaga, the feet are organized, as in the ordinary 

 placental Digitigrndes, they present in the present tribe a variety 

 of well-marked modifications, according to which the species may 

 be arranged into ambulatory, saltatory, and scansorial groups. 



Ambulatorxa. 

 The only known existing representative of this family is the 

 animal described by Mr. Waterhouse, which constitutes the type of 

 his genus Myrmecobius, of which the following is the remarkable 

 dental formula : 



Incisors ^ ; canines ,-^ ; prsemolares 3^3 ; molares g^* : = 52. 



From which it will be seen, that the number of molares, sixteen 

 in the upper and eighteen in the lower jaw, exceeds that of any 

 other known existing Marsupial, and approaches that which charac- 

 terizes some of the insectivorous armadilloes. The resemblance to 

 Dasypus is further carried out in the small size of the molares, their 

 separation from each other by slight interspaces, and their implanta- 

 tion in sockets which are not formed by a well-developed alveolar 

 ridge. The molares, however, present a distinct tuberculate struc- 

 ture ; and both the true and false ones possess two separate fangs 

 as in their Marsupial congeners : they are, however, the least pro- 

 duced of any Marsupials ; only the triturating tubercles appearing 

 above the gum. 



The false molares present the usual compressed triangular form, 

 with the apex slightly recurved, and the base more or less obscurely 

 notched before and behind. The canines are very little longer than 

 the false molares ; the incisors are minute, slightly compressed and 

 pointed ; they are separated from each other and the canines by 

 wide intervals. 



The Myrmecobians are insectivorous, and shelter themselves in 

 the hollows of trees, frequenting most, it is said, those situations 

 where the Port Jackson Willow abounds. In the structure and 

 proportions of the hinder feet, Myrmecobius resembles the Dasyurine 

 family ; and in the slightly developed canines, the smooth external 

 surface of the skull, the breadth between the zygomata, and the 

 absence of the interparietal ridges, as well as in the general exter- 

 nal form and bushy tail, it offers an especial approximation to the 

 genus Phascogale. 



Intermediate however to Myrmecobius and Phascogale would 

 seem to be the station held by the interesting extinct genera 

 above alluded to. In Phascolotherium the affinity is manifested in 

 the simple form, small size, and straggling disposition of the inci- 

 sors and canines : in the other genus, Thylacotherium, it is dis- 

 played in the size and number of its molares. 



This, one of the most ancient mammiferous genera hitherto dis- 

 covered, presents eleven molares on each side of the lower jaw, which 

 resemble in structure and close arrangement those of Phascogale 

 and Didelphis, while they are intermediate in their proportional 



