MUSEUM OF COMPARATIVE ZOOLOGY. 5 
and one on the symphysis. Behind the teeth proper, on each jaw there 
is a patch of scales similar to those on the lips at the angle of the mouth. 
The anterior row in each of these patches, being somewhat regular, was 
wrongly counted as teeth in the preliminary description. Backward 
the size of the teeth decreases. There is also some change in the shape, 
but the change from teeth with broad base, three cusps, and two but- 
tons, to scales with a single cusp, is sudden and decided; i. e. they do 
not grade into each other. A strong lens, however, is necessary to dis- 
tinguish them, since in the hinder row each cusp looks much like a single 
scale. In the front teeth the median cusp is but little longer than the 
others ; it curves directly backward, and does not extend much beyond 
the prongs of the base. The lateral cusps of the same tooth incline 
laterally and curve backward. The points are slightly bent upward. 
Between the cusps, on the inside of each of the lateral, and on both sides 
of the median, a slight ridge runs from the base toward the apex; it 
also connects with the button. On the outside of the laterals this keel 
or ridge is obsolete, except very near the base. Striations do not appear 
on the first rows of teeth. At the junction of cusp and base the enamel 
is inflated or swollen into a low ridge or collar around the base of the 
cusp; this ridge is marked by slight prominences and hollows, as if folds 
once existing in the enamel had disappeared, leaving only these traces of 
their presence. Anteriorly the cusps are greatly bent back toward the 
base ; posteriorly they are nearly or quite erect. The base is broad and 
long. On its upper side a ridge runs backward behind each of the but- 
tons. These ridges end in a pair of prongs, which extend beneath the 
base of the next tooth in the row. In front of the prongs, between their 
bases, a small pore marks the opening of a vessel which, descending for- 
ward, passes to the lower side to reappear in the anterior portion of the 
tooth’s base. Excépt at the opening of this vessel, the groove, from the 
notch between the prongs and forward under the base, is not open as 
figured in Plate VI.; its covering, however, is translucent, very thin, 
and easily carried away. On each side of the ridge in which this groove 
lies there is a concavity for the reception of the basal prongs of the pre- 
ceding tooth. Outside of each of these indentations there is a rounded 
prominence which is situated beneath the base of a lateral cusp. About 
a third of the length of the base of each tooth extends under that of the 
next behind it in its row. 
Backward the characters of the teeth change. In the sixth and 
seventh rows the little prominences around the base of a cusp have 
become snailow plications or foldings in the enamel, which in the ninth 
