STATE GEOLOGIST. 183 
Its section is sub-triangular, the outer and lower surfaces being rounded, 
while the upper and inner surfaces are flat or slightly concave. The exte- 
rior curved surface is grooved longitudinally, with 18-20 grooves, which are 
about twice as wide as the ridges they separate. They are unequally dis- 
tant, being more close on the lower side than on the outside. The inside 
and upper side are not thus grooved, but they show fine transverse waving 
undulations of growth, which also are sometimes visible crossing the grooves 
and ridges of the exterior surface. At the extremity, which seems to have 
run nearly to a point (now broken off) rather than to an edge, the enamel is 
worn away by use on the upper side about an inch from the end. There is 
a large duct or canal entering the ramus about an inch back of and above 
the fourth molar, which, passing the fourth molar without bifurcation, 
descends obliquely over the incisor outwardly, and passes below the third 
molar. The grinding surface of the molars is concave in the direction of 
its length, as in other specimens that have been described. Its length is 
three inches. Our specimen thus compares with others in the length of the 
grinding surface of the molars : 
The Clyde specimen 2. 1% inches. 
The Nashport specimen 2.8 *' 
The Memphis specimen 3. 1 " 
The Minneapolis specimen 3.0 " 
Prof. A. J, Allen regards the Castoroides so constituting the type of a dis- 
tinct and hitherto unrecognized family [Castoroididcp) and separates it entirel}- 
from the Castondca. In the same group he inclines to include the Amblyrhiza 
and Loxomylus, described by Prof. Cope, from the bone caverns of Anguilla 
Island, West Indies. This rodent, he says, "presents a singular combina- 
tion of characters, allying it, on the one hand, to the beaver, and on the 
other, to the chinchillas and viscachas, and also to the muskrat, but which at 
the same time separate it widely from either group." 
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