178 DE, B. A. BENSLET ON THE EVOLUTION 



derivation from the same type. Fotorous has retained primitive characters by assuming 

 a more or less fossorial habit, while the remaining genera Bettongia, jEpyprpmms, 

 and Caloprymnus, of both subfamilies, have, like the Maeropodinje, assumed a freer 

 ground-living habit, with tlie development of a more elongated saltatorial modification in 

 the pes. 



Passing to the Macropodinse, we find two chief types, respectively characteristic of 

 the arboreal forms (species of Bendrolagiis) and the terrestrial ones. The pes of Dendro- 

 Jagus (PI. 7. fig. 22) is comparatively short. The proportion of breadth to length in a 

 spirit-specimen of I), uyslniis and also in a skeleton of I), iiinstm Avas found to be approxi- 

 mately 1 : 3. This appears to indicate a more primitive condition than even in Sypsipnjm- 

 itodon, where, disregarding the hallux, the proportion is about 1:6; but it is very 

 probable that the shortened condition of the pes has been reacquired. The plantar surface 

 shows no indications of pads. Tliese, like the hallux, have been lost during the antecedent 

 terrestrial phase. Tlie second, third, fourth, and fifth digits resemble more clos(4y those 

 of the Phalangeridae than those of the terrestrial Maci'opodinse, and similar conditions 

 characterize the metapodials and phalanges in the skeleton. In the fourth and fifth 

 digits the claws are definitely curved. It is difficult to state exactly how far these 

 characters have been secondarily developed or have been carried over from the phalan- 

 gerine ancestors through a primitive tei-restrial form. As to whether there is a special 

 resemblance between Borco2)sis and Bendrolagus in foot-structure as there is in dentition 

 has been difficult to ascertain from a comparison of the available specimens, all of those 

 representing the former genus being dried preparations. The general conformation of 

 the pes in Lorcopsis is as in other terrestrial macropodine forms. The ratio of breadth 

 to length is aj)proximately 1 : 7-9, the foot being relatively short as in Potorous. It is 

 nn interesting fact that the pes of D. luctuosa presents a distinctly swollen condition as 

 compared with that of D. Muelleri or I). Macleayi, and the heel, and in fact the whole 

 pes, is less elongated than in the latter species. These characters point to those of 

 Dendrolagxis, and afford some evidence for the conclusion arrived at from a study of the 

 dentition, namely, that Dorcopsis is a secondary terrestrial derivative of the secondarily 

 arboreal Bendrolagus. 



The members of the macropodine series, Fetrogale, Onychogale, Lagorchestes, Lago- 

 stroplius, and Ifacropus, show very great uniformity in the general pattern of the pes, 

 and the specimen of Macropus dorsalis here figured (PI. 7. fig. 34) may be taken as 

 I'epresentative of the group. The ratio of breadth to length in this specimen is 1 : 13*5. 

 The fifth and the intimately joined second and third digits are now more closely associated 

 with the fourth, and thus show a great reduction of the free movement characteristic 

 of more primitive plantigrade forms. The fourth digit is perfectly axial in position, and 

 corresponds very closely in stoutness with the middle portion of the foot. The plantar 

 surface is covered with a tuberculated skin, and of the plantar pads the marginal as well 

 as the hallucal one has completely vanished ; while the thi-ee digital pads are completely 

 fused together, forming a prominent protuberance which shows not the slightest traces 

 of the striated areas formerly present. 



Comparison of the proportions of the feet in the various genera reveals a slight 



