I 



NOTOTHEEIID^. 161 



Family NOTOTHERIID^. 



Dentition : — 1. 1, C. ^, Pm. j, M. ^. The cheek-teeth are rooted, 

 and the upper true molars carry two transverse ridges, which 

 are not connected by a longitudinal bridge ; the premolar is tri- 

 angular, small, and apparently had no predecessor. In the lower 

 true molars the unworn ridges are sometimes subcrescentoid, and 

 partially connected by an incomplete longitudinal bridge (^o. 

 43523). The upper incisors of the two sides are widely separated 

 and are of moderate size ; while the lower incisor is procumbent 

 and of the same relative proportions. The preorbital part of the 

 cranium is very short; the extremities of the bones roofing the 

 nasal cavity are expanded laterally, and the zygomatic arches are 

 enormously wide. There are no palatal vacuities. The mandibular 

 symphysis is anchylosed ; the inferior border of the ramus highly 

 convex, the condyle like that of Phascolomys, and the masseteric 

 fossa without pit or perforation. The limbs are of equal length ; 

 the humerus ^ has an entepicondylar foramen, and closely resembles 

 that of Phascolomys; the olecranon is well developed, and the 

 other limb-bones and vertebrae are of the type of those of the 

 latter genus. The structure of the feet is not fully kuown, but it 

 apparently approximated to that of Phascolomys, 



This family connects the Phascolomyidce with the Diprotodontidce ; 

 the cranium, limb-bones, and vertebrae being nearest to those of 

 the former, the mandible showing characters common to the two, 

 while the cheek-teeth are of the type of the latter. 



It is easy to see how the structure of the cheek-teeth could 

 pass into that of the Phascolomyidce ; and it is not improbable 

 that the two families may have diverged from a common ancestor. 

 The structure of the humerus apparently indicates fossorial habits. 



Genus NOTOTHERIUM, Owen I 

 Since this is the only known genus, its characters are the same as 

 those of the family. 



1 De Yis (Proc. Linn. Soc. N. S. Wales, vol. viii. p. 404) has provisionally 

 referred another type of humerus to Notothermm. That bone probably, how- 

 ever, belonged to a small Diprotodon ; and there is everj- reason for regarding 

 Owen's determination as correct, smce there is no dental evidence of the existence 

 of any other animal to which the bones referred by Owen to tlie present genus 

 could have belonged. The great difference between the skulls of Diprotodon 

 and Notothermm would of itself indicate that an equally well-marked difference 

 should occur in the limb-bones of the two genera. 



=2 Cat. Foss. Mamm. and Aves Mus. E. Coll. Sm-g. p. 314 (1845). 



PART V. m: 



