688 The Tertiary Marsupialia. [July, 
In all three of these families the incisor teeth are in reduced 
numbers, and are constructed on the rodent type, with an exter 
nal band of enamel. They thus approach the genus Phascolo- 
mys (wombat), one of the Poéphaga of the existing Australian 
fauna. The genus Tritylodon (Fig. 2), recently described by 
Owen, is from the South African Trias. It is a remarkably spe- 
cialized form, considering its geological antiquity. Its form 
above is, I. 2; Pm. 4; M. 3. The lower jaw is unknown. The 
median incisors are developed at the expense of the laterals, and 
are separated by a wide interspace. There is also a maxillary 
diastema. The molars and last premolars all support three rows 
of shortly conic tubercles (Fig. 7 4). The genus Stereognathus 
Ney f 
| J size; from 
anterior part of skull, wag 
Fic. 2.—TZyitylodon longevus Owen, below: 2, fram shor 
the Triassic beds of S. Africa. Fig. a, from 
Quart. Journ. Geol. Society, 1884, p. 146. : 
Charlesw., includes species from the English Oodlite. 
molars have three longitudinal rows of crescentic while tte 
6). The species are no larger than a small shrew, ak 
skull of Tritylodon longavus is as large as that ofa m 
formation as to the structure of the skeleton of these | 
forms has not yet been obtained. : 
There is on sa genus of the Polymastodontic®, oe 
todon Cope. It is known from three species, all pe has bons 
Eocene of New Mexico. The largest, P. soe majt. 
equal in size to those of the large kangar a p 5 jarge 
The jaw of the smallest species, P. foltatus (Fig. 5 io PI 
that of Hyrax capensis; that of the third speci®» o 
The know? 
cles (Fig: 
