108 DK. B. A. BENSLEY ON THE EVOLUTION 



transversely striated. The sole is completely naked. The ballucal pad is subdivided 

 and its posterior portion m oderately elongated. 



Basyurus niaculatns is represented in tlie collection only by dried skins. So far as 

 can be judged from these, the pes practically repeats the arboreal type of D. liallucatus. 

 The plantar jiads are well developed and transversely striated. The proportion of 

 breadth to length is 1 : 4. The hallux appears to be relatively more reduced than in 

 I), liallucatus. 



The terrestrial forms Basyurus Geoffroyi and vicerrinus, on the other hand, show 

 resemblances to Clioitocercus and Basyuroides. In the former the proportion of breadth 

 to length is 1 : 4-7. The hallux is relatively smaller than in B. liallucatus. The digital 

 pads are partially fused together, and their surfaces are completely granular. The 

 hallucal and marginal pads are entii'ely absent. The posterior ^Jortion of the sole is 

 hairy, as iu Chcetocercns. In Basyurus viverrinus (PI. 7. fig. 11) we find a direct 

 advance on the terrestrial type of D. Geoffroyi. The pes is more elongated, the 

 proportion being 1 : 6. The marginal fur of the foot tends to encroach to a greater 

 extent on the sole. The digital pads are still more definitely fused, and the hallux has 

 disappeared. 



In all of the terrestrial forms above described, with the exception of Phascogale 

 macdonnellensis, the tendency is towards digitigrade modifications. In Sarcopliilus 

 (PI. 7. tig. 12) plantigrade conditions have been retained, the foot being relatively short, 

 as in Fhascogale, the proportion of breadth to length being in the neighbourhood 

 of 1 : 3"5. The hallux is absent, as in other advanced terrestrial forms. There 

 are no plantar pads, the sole being uniformly covered with a papillated skin. The 

 whole condition is unique in the family, but is derivable from an arboreal Dasyurus 

 type. 



In three of the four terrestrial lines here recognized we have animal*^ of respectively 

 small, medium, and large size showing the same type of foot-modification. This 

 ."ippears, at first sight, to indicate genetic sequence, but such a view is rendered 

 improbable by the fact that the evolution of the family is primarily an arboreal one, and 

 that in the arboreal series we have animals of successively larger size. The terrestrial 

 lines have arisen in succession with the development of larger and larger species in the 

 arboreal series. It, furthermore, seems impossible to regai'd the generic characters of 

 Basyurus as the result of convergent development in t\\o sets of species, one of 

 arboreal, the otlier of terrestrial derivation, as we should be obliged to assume in 

 adopting the former view. 



The foot-structure of the terrestrial form Myrmecohius is, in many respects, unique, 

 and there is little in the way of direct evidence concerning its relations with the 

 Fhascogale type. The proportion of length to breadth is 1 : 5-5, the foot being thus 

 slightly elongated. The sole is naked anteriorly and provided with a smooth tough 

 skin ; its posterior portion is hairy for about 12 mm. forwards. There is no external 

 hallux. An oval elevation in the region of the tip of the reduced hallucal metatarsal bone 



