OF THE AUSTRALIAN MARSUPIALIA. 14.9 



to show a tendency towards extension to the remaining cusps. This development is 

 continued in the Macropodinte with the rapid ohliteration of the originally cuspidate 

 character. It is associated ^ith a vertical lengthening of the newly formed crests, and 

 the partial conversion, in most cases, of the internal longitudinal bands of the 

 upper teeth, and the corresponding external hands of the lower teeth, into longitudinal 

 crests. 



Incisors. — In Potorom plafi/ops these teeth are much as in Petaurus. The median 

 upper incisors are prolonged beyond the otliers, and are also stout, gently curved, and 

 slightly flattened. The second upper teeth are small, and act as a stop for the lower 

 teeth, while the third are flattened and have their cutting-edges elongated. The lower 

 incisors are not greatly elongated as in Petaurus, but have their tips gently curved 

 upwards as in that form. 



Passing through the remaining species of Potorous, we find much the same conditions 

 as in P. plutyops, except that the median upper incisors become slightly straighter, 

 stronger, and more angular, the second teeth larger, and the lower teeth straighter and 

 n.ore elongated, so as to project forwards but only slightly upwards. 



The incisors of Caloprymnus resemble those of P. plati/ops, but show some characters 

 pointing towards the Macropodinse. These relate chiefly to the tendency of the median 

 upper teeth to become flattened so that their edges shear against the tijjs of the lower 

 teeth instead of simply piercing against them. Both the second and third upper teeth 

 serve as a stop for the lower ones, but show a slight tendency to shear against their 

 sides. The latter show much the same proportions as those of P. plati/ops. 



Canines. — These teeth are reduced, but not wholly vestigial, in all of the species of 

 Potorous, as in the Bettongiinae. In Caloprymnus they are quite vestigial, more so, in 

 fact, than in many of the Macropodinge. 



Median and posterior Premolars. — As in the case of the Bettongiinae, these teeth 

 furnish the most valuable indications as to the direction of the dental evolution. Unlike 

 those of the latter division, their axes are never rotated, but are always placed in a line 

 with the molars, as in Macropodime. In Potorotis platyops the posterior premolars are 

 extremely simple. The upper teeth are small ; their edges are emarginate and bear two 

 short superficial grooves. In P. Gilbertl these teeth are more elongated, and the number 

 of grooves is increased to three. In P. tridacti/lus (N.S.W.) the teeth bear three grooves 

 and indications of a fourth, while in the Tasmanian form, P. aplcalis, there are four 

 fully developed grooves. In both of the latter species the teeth are still more elongated. 

 In the lower teeth a similar sequence is observable. In P. plati/ops and P. Gilbertl 

 there are two grooves, in P. tridadi/lus and P. aplcalis there are three with indications 

 of a fourth. The dwarfed Tasmanian form (P. rvfus) shows three grooves in both upper 

 and lower teeth. 



In Caloprymnus (PI. 5. figs. 33, 37) the posterior upper premolars are slightly 

 elongated, and the edge bears two superficial grooves, with indications of a third. 



21* 



