154 Cincinnati Society of Natural Fistory. 
with an oval depression a little above the center. Farther back in 
the series the depressions are central and circular. 

Fic. 14.—One-third natural size. Caudal vertebrae, upper side: a, the first; b, the 
fifth. 
The centra are the longest in the region of the tenth to the four- 
teenth, as in Castor. The eleventh is 1.75 inches. ‘They are not 
flattened vertically, as in Castor, till we reach the seventeenth, the 
distal end of which is .66 of an inch laterally, by .65 vertically. 
The neural spines are proportionally of about the same length 
as in Castor, and fade out backward, disappearing in the eighth 
orninth. ‘They are relatively thicker and stouter in Castoroides, 
the first being more than half an inch thick at the summit, and 
I.12 inches antero-posteriorly. 
The transverse processes are relatively shorter than in Castor, 
and have not on their outer extremities the spurs or spines, which 
are a marked feature of a few of the forward tail vertebre of well- 
matured specimens of the latter. 
They are not directed backward, as in Caséor, from the third to 
the seventh, but are deeply notched or falcate on the anterior bor- 
der next the centrum, from about the fourth to the twelfth. In 
this lateral feature the genera are similar. ‘There is also a marked 
similarity in the broad, wing-like, bifurcate character of the trans- 
verse processes seen from the ninth to the twenty-second in Castor, 
and from the ninth backward in Castoroides. Asa rule, the ante- 
rior division of the flattened lateral process is much larger, and is 
directed forward, while the smaller is directed backward. These 
are particulars which are liable to differ in the same species, but as 
none of my readers may have seen the tail of Custoroides, it may 
be of value to notice the particulars, especially as this part of the 
skeleton is indicative of the creature’s habits. 

4 
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