258 
On the Dentition of Sciuropterus. 
[Aug. 
on each side of either jaw, and nearly equal in size, with their crowns surmounted 
by elevated lengthened tubercles, variously disposed in those of the upper jaw, 
and in the lower, forming on each tooth, a kind of circular rim surrounding a cen- 
tral depression.” 
The only specimens of the tribe in my possession, are of the S. maximus and 
S. palmarum , and the teeth of both species differ from those which I have attempt- 
ed to describe, in the following particulars : — 
1- — The lower incisors of Sciurus are long, extremely sharp, and with a flat 
internal surface, gradually attenuating them from the base, where it joins the 
gums to the apex : — but those of Sciuropterus are comparatively short, and flat- 
tened at the apex by attrition against the upper incisors ; the internal surface 
being concave. 
2. — In Sciurus the first molar of the lower jaw is similar to the other three; 
but in Sciuropterus it differs from them, in having the most prominent tubercle of 
its upper surface on the anterior and outer, instead of the anterior and inner side. 
3. — In Sciurus the grinding surface of the molars of the lower jaw is smooth, 
being filled up level, or nearly so, with the folds of the enamel : but in Sciurop- 
terus there is a depression, more or less deep, between every fold, giving an 
appearance of roughness to the tooth. 
4. — In Sciurus the first molar of the upper jaw is not larger than the last, and 
it is much less than the second and third : but in Sciuropterus this tooth is much 
larger than the last, and nearly, if not quite equal in size, to the second and third. 
5. — In Sciurus the enamel of the molars of the upper jaw is disposed in tuber- 
cles (or elevated ridges, with here and there a tubercle), around and upon the crown 
of the tooth : but in Sciuropterus there are elevated ridges of enamel ranged 
across the tooth : from the outer to the inner side, where they are pinched up, as 
I before mentioned, to form a pyramidal, crystalliform tubercle. 
6. — In Sciurus the fangs of the upper molars are generally less divergent than 
those of the same teeth in Sciuropterus : and the inner one is not so large com* 
pared with the outer two, nor so much curved as in the latter genus. 
The question here arises, can these points of difference be owing to “ detrition 
of the crowns of the teeth ? The following facts are against this supposition. 
Detrition alone could not produce and maintain the change of form shown in 
the incisors of Sciuropterus. 
The different arrangement of the enamel of the teeth could not arise from 
detrition. 
Detrition could not effect a change in the relative size of the teeth. 
And finally the effects of detrition become more perceptible as the animal ad- 
vances in age : but my specimens of Sciurus were both younger animals than the 
one of Sciuropterus, and consequently their teeth could not owe their comparative 
smoothness to this cause alone. 
Such are the facts which appear strongly to confirm M. F. Cuvier’s division of 
the Oriental Flying Squirrels from those of Siberia and the New World; and it 
makes not against this division that Baron Cuvier omitted it, unless it can be 
shewn that he had specimens of each kind before him, when he formed his genus 
Pteromys . 
Some stress may also be laid upon Button's remark, confirmed as it has been, by 
succeeding Zoologists*; that the animals of the Old World are not found in the 
* Th “ 1ms latterly been denied, but the examples to the contrary are so feu and 
ral rule “ ' ’ Sh ° UM ^ lo ° ked u P on as exceptions than a gene- 
