15 



character, with the modification of the tail, induced M. Desmarestto 

 separate the Pigmy Petaurist from the rest of the species, and con- 

 stitute a new subgenus under the name of Acrobata. 



In four adult specimens, and two of which had young in the pouch, 



• • 3 — 3 



I find the following dental formula to be constant ; — incisors ^^ ; ca- 

 mnes j^; prsemolares ^3; molares ^^^ : =36. 



The three quadricuspidate grinders of the upper jaw are preceded by 

 three large spurious molares, each of which has two fangs, and a com- 

 pressed, triangular, sharp-pointed crown, slightly but progressively 

 increasing in length, as they are placed forwards. An interspace 

 occurs between these and the canine, which is long, slender, sharp- 

 pointed, and recurved. The first incisor is longer than the two be- 

 hind, but is much shorter than the canine. In the lower jaw the 

 true molares are j^receded by two functional false ones, similar in 

 size and shape to the three above ; the anterior false molar and the 

 canine are represented by minute, rudimental, simple teeth ; the single 

 incisor is long and procumbent, as in the other Petaurists. 



Genus Phascolarctus. 



The absence of anomalous spurious molares and of inferior canines 

 appears to be constant in the only known species of this genus. The 

 dental formula in three of this species, {Phase, ftiscus Desm.,) is: 

 Incisors j^j ; canines ^^; prsemolares j— ; molares ^-::^ : =30. 



The true molares are larger in proportion than in the Phalangers ; 

 each is beset with four three-sided pyramids, the cusps of which wear 

 down in age ; the outer series in the upper teeth being the first to 

 give way ; those of the lower jaw are narrower than those of the 

 upper. The spurious molares are compressed, and terminate in a 

 cutting edge ; in those of the upper jaw there is a small parallel 

 ridge along the inner side of the base. The canines slightly exceed 

 in size the posterior incisors ; they terminate in an oblique cutting 

 edge rather than a point, their fang is closed at the extremity ; they 

 are situated as in the Phalangers close to the intermaxillary suture. 

 The lateral incisors of the upper jaw are small and obtuse, the two 

 middle incisors are of twice the size, conical, subcompressed, beveled 

 off obliquely to an anterior cutting edge, but difi:ering essentially 

 from the denies scalprarii of the Rodentia, in being closed at the 

 extremity of the fang. The two incisors of the lower jaw resemble 

 those of the upper, but are longer and more compressed : they are 

 also formed by a temporary pulp, and its absorption is accompanied 

 by a closure of the aperture of the pulp cavity, as in the upper in- 

 cisors. The Koala therefore, in regard to the number, kind, and con- 

 formation of its teeth, closely resembles the Phalangers, with which 

 it agrees in its long caecum, but the stomach has a cardiac gland as 

 in the Wombat. The extremities of the Koala are organized for 

 prehension ; each is terminated by five digits ; the hind feet are pro- 

 vided with a large thumb, and have the two contiguous digits enve- 

 loped in the same tegumentary fold ; the anterior digits are divided 

 into two groups, the thumb and index being opposed to the other 



