1888.] O. Thomas —Eupetaurus, a new form of Flying Squirrel. 257 



Of the three specimens before me I propose to call the two received 

 from Mr. Lydekker and Mr. Giles together the co-types, the descrip- 

 tion of the external characters and the coloured plate being founded on the 

 former, as the largest and finest specimen of all, while the latter has 

 furnished the particulars for the description and figures of the skull and 

 teeth. 



EuPETAURUS, gen. nov. 



Externally as in Pteromys, except that the claws do not possess the 

 exceeding sharpness characteristic of all previously known floating 

 mammals.* 



Skull distinguished from that of Pteromys by its longer, trumpet- 

 shaped muzzle, more marked supraorbital notches, longer anterior pala- 

 tine foramina, and shorter bony palate. 



Teeth strikingly contrasted with those of any of the other 8ciurid.ce 

 by being hypsodont instead of brachyodont, while their essential pattern 

 remains unchanged. Thus, while the crown of each tooth is enormously 

 lengthened vertically, the grooves ordinarily present on the grinding 

 surface of the molars of Pteromys are reproduced as deep vertical in- 

 foldings of the enamel, which, when seen in the natural section produced 

 by wear, give the teeth very much the general appearance of those of many 

 of the Hystricomorpha. Owing to the worn state of the teeth in the 

 single skull available, it is impossible to say how many extra superficial 

 grooves there may have been, but of the deeper notches there are two on 

 the outer and one on the inner side of each cheek-toothf above, and two 

 on each side of each tooth below, the anterior internal notch, however, 

 in the posterior teeth almost worn out of sight. The teeth also, apart 

 from their hypsodont structure, are distinguishable by their very large 

 proportional size, by being set more obliquely than is the case in other 

 squirrels, and by presenting, in cross-section, a sharp postero-internal 

 angle, markedly different from the evenly convex internal border of the 

 teeth of Pteromys. The implantation of the large upper premolar is also 

 peculiar, in that of the three distinct roots it has in the allied forms 

 the antero-external and the internal have coalesced into a single broad 

 flat root running along the whole of the long antero-internal border of 

 the tooth. 



* Whether Flying Phalangers, Flying Squirrels, or Galeopitheci, this sharpness 

 of the claws is obviously an adaptive character of the highest utility to an animal in 

 the habit of taking long flying leaps from tree to tree and yet without tho Bat's or 

 Bird's power of saving itself from a more or less serious fall in case it fails to secure 

 its hold on the tree towards which it is leaping. 



t Excepting of course the small cylindrical penultimate premolar. 



