me 
1871,] [Cope. 
direction, This curvature is seen in teeth of WV. jeffersonii (See Leidy’s 
Memoir on Extinct Sloth tribe, Pl. VI., figs. 4-6), which do not appear 
to be straight in the maxillary bone at least, at any time. These teeth 
differ from those of I. jeffersondi in having the posterior margin thinned 
ut, while the anterior is thickened by the near aproximation of the 
interior rib. In the larger of the two the posterior margin is slightly in- 
curved, the exterior convexity thus produced opposing that of the anterior 
face and inner rib, as one short side of a romboid does that opposite to it. 
The section of the smaller differs in the shortness of this intero-external 
face, and is thus rounded subtriangularly and antero-internally, as de- 
scribed by Leidy in the IZ jeffersondi, and thus different from that seen 
in the W. wheatleyt. The external face has an open longitudinal con- 
cavity, The triturating surface in both teeth is a longitudinal groove ; 
in the larger, the inner margin is highest anteriorly, the outer highest 
posteriorly. 
These teeth I suppose to represent a species different from the J/. 
wheatleyi, and perhaps from the M. jeffersonti also, as none of the sections 
given by Leidy (1. c. Pl. XVI), approach their form. The nearest is his 
fig. 8, where the section of the bulge is not quite central. 
MEGALONYX WHEATLEYI, Cope. 
Species nova. 
Represented especially by fourteen canine and sixteen molar teeth, but 
probably also by the greater part of the bones above mentioned. The 
former are referable to eight individuals, to which perhaps four others 
should be added. 
The characters of the species are chiefly visible in the molar teeth, 
which in the maxillary bone are acutely trigonal instead of triangular 
ovate as in the MW. jefersont?; and in the dentary bone, transversely, 
sometimes narrowly, parallelogrammic, frequently narrower internally 
than externally. In the W. jeffersonii the latter are almost as broad as 
long, of equal width, and with the inner or outer margin slightly oblique.” 
In the cantne-molars before mentioned of the second and third types, 
Wwe have but little or no curvature of the shaft, no longitudinal grooving 
of the outer face, the outer dentinal wall uniformly higher on the tri- 
turating surface than the inner, and the long diameter of this face but 
little oblique to the transverse plane of the shaft. As both superior and 
inferior molars corresponding in size, color, and number to these teeth 
have been found, I suppose the latter to have been derived from both 
Jaws, 
The differences in these teeth are to be seen in the different degrees of 
development of the dentine layer, and of the bulge on the inner face, and 
of the degree of compression of the shaft. Five of the best preserved ex- 
hibit the thickness of the external layer continued round the extremities 
of the grinding surface, and then rather abruptly contracting wedge like, 
into the thin layer of the interior face. In two other teeth this con- 
traction takes place at the external curves, and is less in degree, the inner 
