TOXODONT CLASSIFICATION 89 
Rhynchippidae 
This family name is used for the three genera Rhyn- 
chippus, Morphippus, and Eurygeniops, which made up a 
part of Ameghino’s family, Notohippidae. ‘These forms I 
find much simpler than Coresodon, Interhippus, Stilhippus, 
and Nesohippus, which, by their molars, should be asso- 
ciated with Nesodontidae, unless it should prove that they 
did not have the incisors enlarged to caniniform teeth, in 
which case another disposition will have to be made of 
them. Ameghino places the Rhynchippidae among his 
Hippoidea, leading to horses, but we found a nearly com- 
plete skeleton of Rhynchippus equinus which in all particu- 
lars is typically toxodont. In the Deseado we found 
fourteen specimens belonging to this family, and strangely 
enough they were all Rhynchippus, and all of the species 
R. equinus. 
This family is distinguished by the brachydont, or 
nearly brachydont, molar teeth, being relatively simple, 
and the secondary cristae not being developed. The large 
basin in the upper premolars and molars is, therefore, not 
subdivided, but is deep, and rather narrow, usually ap- 
pearing as an oblique pit in the centre of the crown. There 
is no enlargement of the incisors to make caniniform teeth. 
Both the upper incisors and the canine have in the crown 
a longitudinal groove, which on wear becomes a pit, and 
being shallow may disappear entirely. The lower teeth 
are those typical of all toxodonts. The feet are tridactyl, 
and compact. 
The following three genera may be distinguished: 
RHYNCHIPPUS MoORPHIPPUS EURYGENIOPS 
ST AGS Sears 31 43 
Formula Se as Oe 
Si ATS x LAS 3143 
Skull moderately long muzzle short muzzle, with short heavy muzzle, 
slight constriction be- | with marked constric- 
hind canines tion behind canines 
Upper incisors groove or pit groove or pit groove or pit 
