28 Cincinnatt Society of Natural History. 
One very striking feature is the ribbing and fluting of the 
enamel throughout the length of the tooth. 
The ribs are about a line in width on an average, and half as 
high, and the flutings or spaces between them are not of uniform 
width, but would average about three times the width of the ribs. 
Three inches from the base we count forty-two ribs in making 
a circumference; near the middle we count thirty-one, and at the 
base of the beveled crown twenty-five. 
Many of these ribs fade out on the surface as we pass from base 
to apex, while a few of them become confluent with the nearest 
one on either side. The lengthwise sinus on the flatter side has no 
rib in, or crossing, its deeper portion till we near the apex, where 
a single rib falls into the valley from the outer curve. ‘These ribs 
appear the more prominent from their being glistening white, 
especially toward the crown, where they have been polished by 
exposure. 
We often observe in teeth of various species, recent and fossil, a 
tendency to crack and split, especially the canines of dogs, bears, 
boars, lions, etc.,—the same is true, in a marked degree, with the 
incisors of rodents, so that it is difficult, oftentimes, to keep a 
beaver’s incisors entire even for a few. months. And this tooth has 
its well-defined cleavage plane, for, though unsymmetrical, it is 
bilateral. The plane of cleavage is well seen where the base is cleft, 
leaving smooth selvage edges and faces. It is seen equally wellin 
the curved line making the longer diameter of the sections, and 
the same seam shows distinctly running the longer diameter of - 
the crown, and along the part of the inner arch where the tongue 
has rubbed the surface. 
The lengthwise fluting of the tooth is shown, not only in the 
enamel but correspondingly in the outer portions of the underly- 
ing dentine, though in a less marked degree. 
The surface is further marked by many rings at right angles to 
the fluting, giving the surface a corrugated appearance. These are 
more distinct toward the base, but are scarcely discernible past the 
middle. 
They are from one to three or four lines apart, and many of 
them so indistinct as to require the light to fall nearly horizontally 
across them in order to make them visible. Two of these girdles, 
the one about three and the other about six inches from the base, 
are so marked by width and prominence as to suggest the annual 
rings on a cow’s horn. 


