240 
PATAGONIAN EXPEDITIONS I PAL/EONTOLOGY. 
these reports on Santa Cruz mammals, so far as to consider more fully 
the pre-Santa Cruzian representatives of the suborder, with particular 
reference to those of the Pyrotherium Beds, for which Gaudry’s geo- 
graphical term, the Deseado stage , will be employed as more convenient 
(Gaudry, ’06, 107). 
Throughout the suborder the teeth are brachyodont and rooted, never 
prismatic, and most of the genera have them in unreduced number, though 
in the early and prematurely specialized family of the Notostylopidae there 
is considerable reduction in the anterior teeth, the second and third lower 
incisors and the canine being usually absent and the first upper premolar 
is frequently wanting ; Diorotherium of the Santa Cruz lacks p 1 . Typically, 
there is a gradual transition in form from the incisors to the molars, as is 
implied in the name of the genus first described, but there are some ex- 
ceptions to this rule. In Notostylops the first incisor is enlarged and, 
though not growing from a permanent pulp, is yet scalpriform in appear- 
ance. In Leontinia , of the Deseado stage (the reference of which to the 
Entelonychia I strongly question) we find the toxodont feature of prom- 
inent tusks formed by the enlargement of the second upper and third 
lower incisor. Should this genus, when its structure is fully known, 
prove to be a rightful member of the Entelonychia, it would show that 
this curious transference of function had occurred separately and inde- 
pendently in three groups of South American ungulates, the Toxodonta, 
the Entelonychia and in the Proterotheriidae of the Litopterna. 
In the Isotemnidae, though the canines are enlarged in some instances, 
the transition in pattern from one tooth to the next succeeding one is 
very gradual throughout the dental series, while in the Homalodonto- 
theriidae there is considerable variation in regard to the development of 
the canines. In the most ancient known genera of this family, as Thomas- 
huxleya, for example, the general appearance of the dentition recalls that 
of the Eocene Perissodactyla of the northern hemisphere, the canines 
forming stout and conspicuous, though not very long, tusks and the lower 
canine passing in front of the upper one and received into a diastema 
between the latter and the external incisor. Much the same description 
applies to Asmodeus of the Deseado. Subsequently, these tusks diminish 
in relative size and in the Santa Cruz forms the lower canine is hardly 
larger or more prominent than an incisor ; but the upper one is still fairly 
large in what are presumed to be the male animals, much smaller in the 
supposed females. 
