MORPHIPPUS 105 
Rhynchippus medianus Ameghino 
R. medianus Amegh., 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p. 375. 
This third species is intermediate in size between the 
two foregoing. No figure is given, but the following meas- 
urements give the size: 
Upper molar 2, length, 17 mm., width II mm. 
Length of lower molars 1 to 3 40 mm. 
Height of mandible under m. 2 24 mm. 
These figures would indicate a form about 15 [% larger 
/ 
than R. pumulis, and 35 % smaller than R. equinus. 
Morphippus Ameghino 
Morphippus, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 459. 
This genus is very similar to Rhynchippus, with the same 
dental formula, the same grooves in the upper incisors, and 
the same pattern of the premolars and molars. It differs, 
however, in the lower incisors having no cingulum at their 
base, in the upper molars having a shallower basin, and in 
bays 3 and 4 being absent from the lower molars. These 
features simply indicate a slightly less advanced specializa- 
tion, less hypsodont teeth. I do not think that the bays 
are any of them lacking in unworn teeth, but in a less hypso- 
dont tooth, with the pits extending a less distance into the 
crown, all indication of the bays disappears early. 
M. imbricatus is described as the type species, and four 
others have been described, all equal in size to M. imbrica- 
tus, and distinguished by the teeth being slightly more 
compressed, by the external cleft of the lower molars being 
deeper, or by variations in the pits. All these features I 
consider to be either age characters or individual variations, 
so that all five species of this genus are lumped under M. 
imbricatus. 
