OF THE MARSUPIALIA,. 325 
more rapidly in size, as they are placed further back in the jaw: the hinder tooth has 
three tubercles, the rest four ; their apices seem to be naturally blunter than in Pet. Ta- 
guanoides. Between the functional false molar and the incisors there are three teeth, 
of which the representative of the canine is relatively much larger than in the Pet. Ta- 
guanoides ; the first false molar is also larger, and has two roots; the second, which is 
functional in Pet. Taguanoides, is here very small; the first incisor is relatively larger 
and is more produced. In the lower jaw the functional series of grinders consists of 
the four true tuberculate molars only, of which the last is relatively smaller, and the 
first of a more triangular form than in Pet. Taguanoides. The space between the tu- 
berculate molars and the procumbent incisor is occupied by four small teeth, of which 
the one immediately anterior to the molars has two roots, the remaining three are ru- 
dimentary and have a single fang. Among the species exhibiting this dental formula, 
: Gin 7 3—3 Raa ae 
viz., incisors =i canines ;— 3 premolars sar molars Sap = 40: are Pet. sciu- 
reus, Pet. flaviventer, and Pet. breviceps. 
The Pigmy Petaurist differs from the preceding and larger species in having the hairs 
of the tail distichous or arranged into two lateral series like the barbs of a feather ; and 
in having the spurious molars large and sharply pointed; and the true molars bristled 
each with four acute cusps. This tendency in the dentition to the insectivorous cha- 
racter, with the modification of the tail, induced M. Desmarest to separate the Pigmy 
Petaurist from the rest of the species, and constitute a new subgenus under the name of 
Acrobata. 
In four adult specimens, two of which had young in the push, I find the follow- 
— 3—3 | 
canines ae premolars 33 > Mo- 
ing dental formula to be constant ;—incisors a= 3 
=r jas 
lars 3: Sih 
The important difference in the number of the true molares was first pointed out by 
Mr. Waterhouse; it is analogous to that which obtains in the Phalangista gliriformis, 
and renders the parallelism in the modifications of the dental system between the Pha- 
langers and Petaurists remarkably close. 
The three quadricuspidate grinders of the upper jaw of the Petaurus pygmeus are pre- 
ceded by three large spurious molars, each of which has two fangs, and a compressed, 
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 
behind, but is much shorter than the canine. In the lower jaw the true molars are 
preceded 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. 
