

A Skeleton of Great Fossil Beaver, Castorcides Ohtoensts. 161 
The pelvis is badly broken, but enough is left, reliably to deter- 
mine the main points. The sacrurn has been noticed already. The 
pelvis of a beaver, muskrat or ground-hog would greatly aid the 
ordinary reader in picturing the corresponding region of Cas- 
torotdes. 
The innominate bones in the four genera, omitting the pubic 
portion, consist of a pair of irregular, shaft-like pieces, whose axes 
are approximately parallel to each other, and to the spinal column. 
The posterior borders of the iliac turn downward nearly at right 
anzles toward the symphysis pubis; giving the posterior part of the 
united innominata a nearly square, truncated appearance, except 
that in Custoroides this posterior region is more rounded back- 
ward. Looking through the entire pelvis from behind, we note a 
pretty well defined triangular cavity. 
The innominate bone, in the absence of the epiphysis of the 
crest, which would add at least one-fourth of an inch, measures 
11.75 inches; tuberosity of ischium to symphysis pubis, 5.3 inches; 
center of acetabulum to back part of tuberosity of ischium, nearly 
4.0 inches; from same point to posterior curve of ischium, 5.8 
inches; same point to anterior symphysis pubis, 4.0 inches; 
greater diameter of obturator foramen, 3.85 inches; lesser diame- 
ter of obturator foramen, 2.12 inches. 
The form of the obturator foramen is approximately ovate, with 
the greater curvature above, asin Castor. 
Each iliac shaft flares outward from about its middle to near its 
crest, where it suddenly projects at right angles, not so much by 
the outward bending of the shaft, as by the outward extension of 
the crest. The measurement across, from point to point of these 
crests, if the epiphyses were present, would not be less than from 
9% to Io inches. 
The shaft of the ilium is triangularly prismatic. The side that looks 
upward is broader than the side that faces downward and outward, 
and both are decidedly concave, not only laterally but antero-pos- 
teriorly. The portion of the inner face in front of the articular 
surface (for the sacrum) is concave in a crosswise direction. Said 
articular surface is about midway of the inner face of the ilium. 
The length of the symphysis pubis can not be determined, as part 
of the connection is missing on both sides. The acetabulum 1s 
nearly hemispherical, the border rising highest in front; antero- 
posteriorly it measures 1.25 inches; vertically it measures 1.2 
inches ; width of cotyloid notch, .5 inch. 
