Lar f 
1871.] i7 [Cope. 
layer being more uniform. In two teeth the dentine of the bulge of the 
inner face is very nearly as thick as that of the outer (F. 4). As regards 
the form, in the last mentioned tooth the bulge is well developed (as in 
Leidy’s Pl. XVI. fig. 1), and the shaft is not compressed. In the two 
previously mentioned, the shaft is short and the bulge very low and 
bounded by two shallow grooves; in one (F. 6) (which is accompanied 
by the posterior molars), it has a shallow median groove. In the five 
canine molars first named we have every degree of compression. In one 
(F. 3) the shaft is stout, and the bulge larger than in any other, about as 
in Leidy’s Pl. XVI. fig. 2; in a second (F. 5) the shaft is similar, with 
low bulge, like fig. 7. 1.c. In the third (#. 7) from a large individual, 
there is more compression, and the bulge is very low ; the last two are 
similar, but sinaller; they belong apparently to opposite sides of the 
same animal (F.8). These are like the tooth figured and described by Dr. 
Leidy as that of Megalonyx dissimilis. 
T am inclined to refer the teeth of these types to one species, a view 
confirmed by a study of the molars. They are all stained yellowish or 
light rust color except one, which is black, and which is associated with 
three posterior molars of similar color and corresponding size. The re- 
maining posterior molars are of the color of the other canine molars, and 
no doubt belong to the same individuals in part, but none can be associ- 
ated with the same certainty as the black specimens. On the light colored 
posterior molars I propose to establish the Meyalonyx wheatley?, since I 
should scarcely distinguish it from M. jeffersonti, or M. dissimilis by the 
canine-molars alone. There can be-no question that the forms of these 
teeth, characteristic of the two supposed species, graduate into each other ; 
the characters derived from the development of the interior enamel plate, 
may be distinctive, but in that case there is at least one other undescribed 
species in the series I have explained above. I. dissimilis it appears to 
me must repose on the posterior upper molar, which Leidy shows to be 
transversly oval and not triangularin section. That tooth is as triangular 
in M. wheatleyi as in M. jeffersonit. 
From the preceding, it is probable that the most allied species of 
Megalonyx, cannot be exactly defined by the characters of their canine 
molar teeth, though, as in many species of Mammalia, they may be in- 
dicated by the extreme forms of those teeth, the range of variation over- 
lapping. 
The supertor-molars (1a) belong to at least three (perhaps four) in- 
dividuals. They are nearly straight trilateral prisms, so worn that the 
inner anterior angle is the most elevated. The anterior dentinal plane is 
slightly convex, the posterior concave to a less degree. The exterior 
angle is much less obtuse than in WM. jeffersonii, that enclosed by the 
dentine being prolonged and very narrow. There is a notable difference 
between the two posterior molars of the superior series, preserved. One 
belongs to the individual stained black. Both are slightly bowed pos- 
teriorly, and both have a subtriangular section, the apex directed inwards. 
