A Skeleton of Great Fossil Beaver, Castoroides Ohioensis. 159 
prominence of the lesser tuberosity is the most marked difference 
I have been able to discover between the humerus of Castoroides 
and that of Castor. 
The wider groove (already named) on the opposite side from the 
bicipital, does not reach down the front face of the shaft, but fades 
out on the epiphysis. 
The front face of the shaft is broadly concave, laterally, nearly 
half way down, owing to the prominence of the deltoid ridge, and 
the swell at the base of the lower or third and outer tuberosity. 
This third tuberosity is a very marked feature, being largely devel- 
oped, much bent backward, and at the extremity slightly inward. 
It is nearly an inch in length, following the curve, three-fourths of 
an inch wide, and very rough on the outside. The deltoid ridge 
is most prominent at base of this process, from which it rapidly 
descends and fades out in the direction of the trochlea. There 
is also a secondary inner tuberosity, very slight, nearly opposite 
the outer, also observable in Castor. 
The olecranal fossa is well marked, but not deep. It is about an 
inch transversely, .3 of an inch vertically, and .12 of an inch 
deep in the center. The longer diameter is not quite at right 
angles with the shaft, the inner end being a little the lowest. 
There is.a fairly well-marked fossa anteriorly, directly opposite the 
olecranal, and parallel with it. The internal condyle is .75 of an 
inch long, the same in width near the middle, very stout, slightly 
bent backward, and has a deep, rough fossa near the base, poste- 
riorly. Said fossa slants under the trochlea. ‘The articular sur- 
face, posteriorly, is .95 of an inch across, anteriorly it is 1.35 
inches across, the most prominent part of the capitellum being 
about midway. The ulna, minus the distal epiphysis, is 8.51 inches; 
the full length was something over g inches. 
The length of the olecranon, from middle of sigmoid cavity, is 
1.75 inch. Thearea for attachment of triceps muscles is nearly an 
inch across. Greater diameter of shaft, two inches from sigmoid 

Fig. 20.—-One-third natural size. Ulna (1) and radius (2). Distal epiphysis wanting. 
