OF THE AUSTRALIAN MAKSUPIALIA. 131 



others wliich can be easily shown from their constant occurrence in the Macropodidse to 

 be of a herbivorons type. As will be seen from a further consideration of the antemolar 

 teeth of this series, the changes noticeable in the incisors of the latter genera are closely 

 associated with others in the premolars which are almost as abrupt in their appearance 

 and are also characteristic of the Macropodidse. 



Functional Canines. — These teeth show a fairly homogeneous evolution. As before, 

 the most jiiimitive conditions are found in the three genera Acrobates, Distoecliunis, 

 and Dromicia. In the two former the teeth are long, curved, and sharply pointed, and 

 are apparently quite as functional as in the Dasyurinte. As will be seen from the 

 flgiu-e of Distcechnnis (PI. 5. fig. 39) they work over the sides of the lower incisors. 

 In both forms they have undergone an anterior progression, so that the space originally 

 occupied by the notch for the reception of the lower canines, and presumably also by 

 additional posterior incisors, lias been obliterated, the third incisors being in close contact 

 witli the canines. In Droniicia the canines are not so well developed, being shorter, less 

 curved, and slightly compressed ; they are also separated from the third incisors by 

 short diastemata. Their shortened condition in this genus represents the beginning of 

 a process of reduction which characterizes the canine evolution in the present series. In 

 Petaurus the canines are so short as to jiroject only slightly beyond the thu'd incisors ; 

 their tips are rounded and laterally compressed. In some cases the compression is 

 accompanied by a grooving of the root as in P. Doreyana, Chceropus, and Myrmecobim. 

 In Dactylojjsila the canines are reduced as in Petaicrns, and are also sUghtly compressed. 

 la Phalange)' we find two diiferent conditions. In P. nrsiniis and P. melanutis the 

 canines are short and rounded as in I>actylopsila, and they project to abinit the same 

 extent as the third incisors, while in the remaining species they are enlarged, in all 

 probability secondarily, and present the cliaracters of normal canines. Trlchosarus 

 shows much the same condition as P. tirsiniis and P. ■nielanotis, the only noteworthy 

 difference being a slightly greater I'cduction. In this form the third incisors frequently 

 project beyond the canines. 



Functional Premolars. — The most primitive conditions are found in Acrobates. In 

 this form the upper premolai's are of a piercing insectivorous type, exactly as in the 

 Dasyurinoe. The resemblance to the latter is increased by the fact that the posterior 

 teeth are slightly reduced as compared with the median, while the latter are slightly 

 larger than the anterior teeth. The lower functional premolars are the median and 

 posterior teeth. They also resemble those of the Dasyurinae in being of a primitive 

 piercing type ; the posterior teeth are again slightly reduced. JJlsta'churus (PI. 6. tig. 39) 

 shows a slightly more advanced stage of the same modification. The upper anterior 

 and median premolars are simply enlarged, while the posterior teeth are still further 

 reduced. In the lower jaw the posterior teeth have entirely disappeared, recalling the 

 condition in advanced forms of the Dasyurinae. The median lower teeth show an 

 elongated and subcaniniform condition. 



The three species of Dronilcla present considerable dilferenccs in their premolar 



SECOND SERIES. — ZOOLOGY, VOL. IX. 19 



