TOOTH-GENESIS IN THE CAVIID®. 285 
evidence is distinctly in favour. of the multituberculate origin 
of the Rodents. 
This leads to a consideration of the fossil Rodents, for a know- 
ledge of which, especially of the South American forms, we are 
indebted very largely to the researches of Ameghino, whose work 
on the fossil mammals of the Argentine [3] forms the source 
from which other writers have largely drawn. Winge [25], 
Schlosser [19], and Forsyth Major [6, 7, 8] have also added much 
that is of value upon the same subject. 
Four genera of the Caviide are reputed to be found in the 
Tertiary and Pleistocene of Brazil and the Argentine. The 
members of this family are easily recognized by their high molars 
composed of two or several triangular prisms which generally 
form straight lamelle, and “determinent une aréte tranchante 
sur la face interne des dents 4 la machoire supérieure, et une 
_ aréte externe 4 la machoire inférieure.” 
From a consideration of the characters of the post-tympanic 
and jugular processes and of the masticatory muscles, Winge 
[25] regards Cavia, Dolichotis, and Hydrocherus as descendants 
of the American Capromyine and places them close to Dasyprocta 
and Oelogenys. Ameghino [8], dividing the Hystricomorpha into 
eight families, places the Capromyide, the Eromyide, and the 
Caviide in close affinity, and these three families together close 
to Octodontide, the points of difference being mainly dental. It 
will thus be seen that these two authorities agree in their general 
conclusions. A careful study of the tooth-pattern of the fossil 
Caviide, as figured by Ameghino, throws but little light upon the 
evolution of the molar crowns, there being apparently but little 
change of pattern from the Eocene, though a comparison of the 
posterior upper molar of Dolichotis from the Pliocene and of 
Cavia shows a reduction in the latter (Pl. 26. fig. 7). 
In the table of genealogical descent suggested by Ameghino 
(Joc. cit.), he would derive Cavia from Hedimys through Paleo- 
cavia, Hocardia, and Phanomys; there is, however, practically no 
difference between the molars of these forms such as would 
throw any light upon the tooth-genesis. If the Euromyide of 
the Inferior Eocene be compared with the later Pliocene forms, 
there is a simplification of the molar crowns though obviously of 
the same pattern. The more so is this the case on comparison 
with the Octodontide. 
