A Skeleton of Great Fossil Beaver, Castoroides Ohioensts. 155 
In the ninth and tenth, the left wing-like process is merely per- 
forated next the centrum, while on the right there is a slit from the 
corresponding foramen to the margin. The eleventh has the fora- 
men on either side, with a groove in place of the slit. The thir- 
teenth and fourteenth have each the foramen in the left wing, and 
an elongated foramen, followed by a groove, which leads to a 
notch in the margin. Numbers fifteen, sixteen and seventeen have 
each the regular cloven character, the divisions diverging from the 
centrum outward. 
The lateral processes are, as a rule, relatively much thicker 
(except in the first three or four) at their outer extremities, than in 
Castor. ‘This is especially so at the anterior borders of the broad 
processes, which are often bent somewhat downward. Without 
these wing-like processes the tail would not present any flattened 
appearance, save near the extremity where the centra are slightly 
compressed vertically. The posterior half of the tail is strikingly 
similar in general appearance to its counterpart in Cas/or, whether 
seen from above or below. 
No chevron bones are preserved, but the prominent processes 
on the under side of all the anterior caudals seem clearly to indi- 
cate that they were there in full size. The median longitudinal 
groove on the under side is very strongly marked. 

Pic. 15.—One-third natural size. Sternum: a, anterior piece: b, posterior extremity. 
Of the sternum but two pieces, the pre-sternum and the xiphi- 
sternum, were obtained. ‘The former is 2.18 inches long, 2 inches 
wide anteriorly, 1.25 inches wide posteriorly, .87 of an inch wide 
near the middle, and is.5 to .75 of an inch thick. ‘This piece is 
relatively more massive than in Cas¢or, and differs materially in 
form. ‘The xiphi-sternum is quite similar to its counterpart in 
Castor, but is relatively somewhat shorter. 
Of the ribs, there are eight right and twelve left, which is prob- 
ably within two of the full number of the latter. Nine of them 
are distinctly tuberculated, but the tenth is not. ‘The length of the 
