1883.] The Extinct Rodentia of North America. 377 
lars are transverse to the axis of the middle portion of the shaft. 
There are but three columns in all of the inferior molars. 
The only caudal vertebra preserved: is short and wide, has 
short diapophyses, and no facets for chevron bones. As there 
is no trace of neurapophyses on the centrum, I infer that the 
tail is short. 
The fore-limb is of smalier proportions than the posterior one. 
The humeral condyles have the ulnar and radial portions about 
equal, and the intertrochlear ridge is repre- 
sented by an obscure angle. Both ulna and 
radius are slender. 
The femur has several marked peculiari- 
ties. One of these is the great development 
of the great trochanter, which is really an 
undiminished continuation of the shaft for 
some distance beyond the head. The head 
is relatively small. 
The distal extremity of the tibia is ex- 
panded inwards, The astragalar facets are 
oblique ; the external is larger than the inter- 
nal, and they are well separated by an obtuse 
ridge. There are two processes on the inter- 
nal border, which are separated by a dee 
‘ : rtion of femur of Am- 
tendinous groove, which is, in most of the blyrhiza latidens, two- 
. > i e ize. From 
Specimens, bridged over by a lamina connect- thirds natural size. «fo 
= , Anguilla, W. I. Orig- 
ing the processes. The posterior of the two inal. 
processes is the most elongate. It corre- ae 
sponds to a process of the astragalus which extends backwards 
and inwards from the internal trochlear face. When extension of 
the foot is attempted, the processes come into contact, and pe: 
vent further movement. The amount of extension from the hori- 
zontal which this arrangement permits is 45°. When the foot is 
extended the processes constitute a support to the weight of the 
animal in addition to that furnished by the usual astragalar apan 
The metatarsal bones are distinct from each other and are quite 
short. There were certainly four toes, and the hallux may have 
been rudimentary. The foot was clearly plantigrade. Whether 
the digits terminate in hoofs or claws, is unknown. 
The lack of tibial crest indicates that the knee was not constantly 
maintained in a flexed position. The immense trochanter indi- 
