OF THE AUSTEALIAN MAESUPIALIA. 97 



not a special character in the Dasyurinae, since it must have been present in the 

 ancestral forms of the Phalangeridye. 



Canines. — These teeth are well developed in all of the Dasyvirina>, but are relatively 

 weakest in Sminthopsis and Antechinomys. In the carnivorous evolution, as exemplified 

 by Phascogale, Dast/m'us, and Sarcopliilus, they present a successive increase both in 

 actual and relative size. The increase in relative size is not at first sight apparent, but 

 is easily demonstrable by sketciung to scale the profile asjject of the tooth-series in such 

 representative forms as Smlntltopsis murina, Phascogale Jlavipes, P. JP'allacei, Dasi/tiriis 

 hullucatus, I), maculatiis, and Sarcophilus ursuius. 



Premolars. — In their general characters these teeth are of the simple piercing type 

 common to the Didelphyidae, Peramelidae, and primitive Phalangeridse {Acrohates and 

 Distwchnrus), as Avell as to the placental Insectivora and Carnivora. In their special 

 characters they present a series of important modifications, Avhich serve to support and 

 extend the plan of dental evolvition as determined by the molars, at the same time 

 throwing light on the relations of the smaller forms with the remaining Marsupials, 

 especially the existing Didelphyidae and Peratherium. 



The chief modifications are as follows : — («) successive reduction of the posterior 

 premolars, proceeding from a stage in which these teeth are the predominant elements 

 of the series {Smiufhopsis and Antechinomys) to one in which they are altogether absent 

 {Dasyiirus, Sarcophilus); (b) compensatory enlargement of the median premolars until 

 tlie reduction of the posterior teeth is completed; (c) subsequent slight reduction of the 

 anterior and median premolars in the final carnivorous stages. 



Some of the features of the premohir evolution of this group have already been 

 described by Thomas (1887), this writer having shown, by a carci'ully selected series of 

 diagrams (pi. 27. figs. 1-5), that the two-premolared condition in Dasyurus is only the 

 culminating stage of a process of reduction of the posterior I'l'eniolars which is 

 exemplified by the species of Phascogale. Thomas has further pointed out that the 

 extent of reduction is always greater in the lower than in the upper teeth, so tliat in 

 certain cases, siich as P. Thorbeckiana and P. apicalis, wliere the upper teeth arc 

 vestigial, the lower may be entirely absent. 



The modifications of the posterior premolars are of great interest, as showing mucli 

 more clearly than those of tlie remaining teeth the primitive position of Sminthopsis and 

 Antechinomys as regards dentition. In both of these genera the posterior upper 

 premolars are always larger than the median teeth, and in some cases [S. leucopiis, 

 A. laniger) disproportionately so, while in Phascogale, with the excejition of P. minalis- 

 sinia, in which they are again disproportionately larger, tliey are variable, being slightly 

 larger than, or equal in size to, the median teeth, or in some cases w lioliy vestigial. As will 

 be pointed out in grciiter detail in a subsequent section, Sminthopsis and Antechinomys 

 make the closest approach to the prototypal condition found in Pe rather inm, Avhere the 

 posterior premolars are apparently always predominant, and, furthermore, they take up 

 a position with reference to the latter genus approximately equivalent to tliat taken by 

 certain of the existing Didelpliyidaj {Peramys). 



