MACEOPODID^. 7 



apparently rounded ofP, and have none of the deep valleys and 

 sharply defined crests so marked in other individuals. This dif- 

 ference may easily be mistaken for one of specific value, especially 

 if by the method of cleaning the skull the cement has become white 

 and shining, and not readily distinguishable by colour or texture 

 from the enamel. During life this cement in some individuals soon 

 gets chipped or worn oif, while in others it persists until the tooth 

 is completely worn down. The only way, therefore, to get at the 

 true character of the molars in such specimens is to chip out with a 

 sharp point the bits of cement filling up the depressions, by which 

 means the valleys and crests are brought into their proper relative 

 prominence. 



The incisors of the Maeropodidce, like many other permanently 

 growing teeth in the Mammalian series, have both a definitely 

 marked non-growing enamel-covered portion, whose size and shape 

 are of systematic importance, and also a constantly lengtheoing 

 dentine root, which, as the crown wears off, may in old animals form 

 very nearly the whole of the tooth. All systematic descriptions of ' 

 the incisors should therefore, and in the present volume do, refer 

 entirely to their unvarying enamel-covered portion. 



Owing to the relatively late development of the posterior molars 

 in this group, the word " adult " cannot be confined, as it is else- 

 where, to individuals with all the molars in place, these being 

 therefore here called " aged," while the word " adult " is used for 

 those in which p.* is in place, although m.* is still below the bone. 

 The late development of m.* was also originally the cause of the 

 choice, as a basis-measurement of the teeth, of the combined 

 lengths of the three anterior molars only ; but the measurement 

 has been found so convenient in the other families also that, as- 

 already noted, it has been adhered to throughout the Order. 



Synopsis of the Genera. 



I. External Chaeaciees. 



A. Hallux absent. Tail hairy. 



a. Size variable, generally large. Claws of fore 

 feet not disproportioDally large, subecLual. 



Ears generally long and pointed .... Subfamily Macropodinae. 

 a'. Back not cross-banded*. 

 a^. Nape-hairs directed backwards t- 

 Form markedly macropine. 

 o'. RhinariumnakedJ. Size variable, 

 generally large or medium, 

 o'. Central hind claw long and 

 strong. Tail tapering, short- 

 haired, rarely crested 1. Maceopus, p. 10. 



* Rarely and very indistinctly banded in one or tvro species of Macropus. 

 t Except, rarely, in two or three species of Macropus. \ 



X Except in Macropus giganteus. 



