ae 
A Skeleton of Great Fossil. Beaver, Castoroides Ohtoensis. 153 
also, has three large transverse openings, but they dzminish from 
before backward. In Castoroides more than enough of the trans- 
verse blades is left to show the perforations corresponding to those 
in the genera just named, and, as in the others, the openings 
b, aseries including ninth to seventeenth. 
a, the seventh ; 
Note the broad transverse processes, some perforate, some notched, others bifureated. 
Caudal vertebra, upper side: 

Fig. 13.—One-third natural size. 
increase in diameter from before back- 
ward. That these side blades widened 
backward is almost certain from the 
length of the transverse processes of the 
first caudal vertebre. 
The articular surfaces, by which the 
sacrum joined the innominate bones, in- 
volves the transverse processes of the 
first vertebra, and over half an inch of 
the second. The entire articular surface 
is 2.75 inches antero-posteriorly, by 1.12 
inches vertically, at the widest part. It 
is difficult to tell just how much of the 
frail margin has been broken off. 
Of the caudal vertebre, fourteen have 
been found. ‘These, laid together in their 
order, making fair allowance for the 
absence of a number of the epiphyses, 
measure, 26.75 inches. As there ane 
three or more missing in the region from 
the fifth to the eighth, the fourteenth in 
hand is about the seventeenth in the 
whole series. ‘lhe abruptness of the ter- 
mination at the seventeenth makes it, as 
compared with the Castor and Fiber, 
seem very probable that the whole num- 
ber was not less than from twenty-three 
to twenty-five. This would give the en- 
tire estimated length of the tail very 
nearly thirty inches, very hkely more 
than less; and the entire length of the 
skeleton, say, five feet nine inches. 
The centrum of the first caudal is 1.25 
inches laterally, by 1.12 inches vertical- 
ly, on the anterior surface, the posterior 
surface being perceptibly greater. ‘These 
articulating surfaces are quite convex, 
