1876.] MR. E. R. ALSTON ON THE ORDER GLIRES. 75 



panying chart (Plate IV.), on which I have endeavoured to indi- 

 cate approximately the relationship of the different families to one 

 another. 



Arrangement. 



Order Glires. 



Suborder I. Glires simplici- Sec. 3. Hystricomorpha. 



Table of Characters. 

 Order GLIRES. 



The middle pair of incisors long, curved, rootless, and constantly 

 growing, their points more or less chisel-edged (except in Mesothe- 

 rium), the other pairs very small or absent ; no canines, a large 

 space intervening between the incisors and the grinding-teeth, which 

 are variously formed ; premolars present or absent ; three molars 

 above and below (except in Rydromys). Skull with the temporal 

 fossae continuous with the orbits, within which the lachrymal fora- 

 men opens ; an interparietal almost always distinct ; the periotic and 

 tympanic ankylosed to one another, but not to any other bone ; and 

 the auditory bullae moderately or largely developed. Scapula nar- 

 row with a deep notch, a well -developed more or less bifurcated 

 acromion, and a small coracoid. Clavicles perfect or imperfect. 

 Scaphoid and lunar usually combined. Manus with five or four digits. 

 Tibia and fibula either separate or ankylosed below. Pes with five, 

 four, or three digits. Intestinal canal long ; caecum large (except in 

 Myoxidce). Liver with a bifid Spigelian lobe (except in Anomalurus) . 

 Placenta deciduate and discoidal. 



Suborder I. Glires simplicidentati. 



Incisors § only, even at birth, their enamel confined to the front 



surface. Skull with both a true alisphenoid and an external ali- 



sphenoid canal* ; optic foramina rarely confluent ; incisive foramina 



separate ; and bony palate well developed. Fibula either ankylosed 



* Of. H. N. Turner, P. Z. S. 1848. p. 65. 



