OF THE AUSTEALIAX MAESLPIALIA. 179 



variation, inasmuch as those of Lagorchestes, Lagostrophus, and Oiiychoyale are re- 

 latively more elongated than those of the remaining species with Avhich they are most 

 closely associated in size. Tiie followiu"- data will suffice to illustrate this difference, 

 although the figures given must be taken as roughly approximate, being based on dried 

 preparations: — Three specimens representing the three species of Onychogale, O.frenata, 

 0. limata, and 0. unguifo'a, show a ratio respectively of 1 : 14.'5-14'6-171 ; a specimen, 

 of Lagostrophus fasciatas, 1 : 151 ; three specimens representing the species of Lagor- 

 chestes, L. leporoides, L. hirsutus, and L. coiispicillatiis, respectively 1 : 15-157-18. 

 On the other hand, specimens representing the species of l^etrogale, P. penlcillata, 

 P. hrachifotis, P. concinna, and P. inornata, show a ratio respectively of 1 : 10"7-10'9- ■ 

 11-8-14 ; while tlie Small Wallabies of the genus Macropiis show a range from 1 : 7 

 {M. Coxeui) to 1 : 13'5 [31. Engenii). In Lagorchestes and Lagostrophus, moreover, the 

 sole of the foot tends to become hairy. 



As regards the three sections of the genus Ilacropiis, namely the Suiall Wallabies, 

 Large Wallabies, and Kangaroos, there is a marked increase in the actual size of the 

 foot as in the size of the body proceeding from one group to the next, and this difference ' 

 has been made use of by Thomas (i888) in defining the three sections. There appears, 

 however, to be no broad differences in the proportions of the feet separating these sections, 

 although it is possible to demonstrate by measurement that the members of the Small 

 Wallaby group show a greater tendency towards the retention of the original shortened 

 form than do those of the other two. This is indeed what we should expect, because 

 while the initiation of a saltatory method of progression demands the development of 

 an elongated pes, yet its perfection is more a matter of the actual size of the animals 

 and the proportion of the hind limb as a whole. 



The species referred to as Setongx brachyuriis corresponds in the proportion of thf^ 

 foot with with the Small Wallabies, the ratio in a specimen measured being 1 : 7 9. 



The Identification of tue Stem-Pokm of the Australian ]\Iarsui>ials. 



So far as deducible from the modifications of dentition and foot-structure, the data 

 already given in the two preceding sections are sutllcient for the construction of a 

 phylogenetic or morphogenetic plan, except in one important particular, namely, that 

 they fail to express the relationships of the primary families Dasyuridaj, PeramelidcV, 

 and Phalangeridae. None of the latter present the ciiaracters of a prototype, such 

 characters being distributed over all three. Thus the Dasyurida; in dentition occupy 

 a prototypal position, except in respect to the upper incisor formula and the characters 

 of the upper molar styles, in which they give place to the Peratuelidic ; while the 

 Phalangeridaj occupy a prototyjjal position in foot-structure, except in the syudactylous 

 condition of the second and third digits, in which they give place to the Dasyuridie. 

 The Australian fauna considered by itself represents a radiation without a recognizable 

 source, and in order to comjilcte it it is necessary to add a hj^pothetical I'orm combining 

 the prototypal characters of the three primary families. 



SECOND series. — ZOOLOGY, VOL. IX. 25 



