Cope.] 84 [April 7, 
preceding this, and concave transversely ; the inner dentinal plate being 
worn much lower than the outer. Exterior face of tooth regularly and 
gently convex. 
M. 
dienath of ivagment of TOObN ies viii. de aie be tea ne ees 0.044 
iigne diamener angrinding tage, Fj ce. aiie ks er, as 025 
cs SS SE DARG. (RO GRtG. tas oat ues ee ates ctu oute ee ee 02°75 
Short ue ee OOS ae TT gis ME ee REG aes 0148 
& - £6 Grinding faves eho id Ce iy ee er eee 0125 
The question has naturally arisen, whether this tooth has not belong- 
ed to a young animal of M. wheatleyi or M. jeffersonit. Its small size and 
subconic form would suggest this view. Teeth of the monophyodont 
type, generally possess the character of those of the successional type, in 
being protruded of the full size, and not increasing in diameter with age. 
Exceptions, however, occur in some Rodentia, as the beaver. It has 
however, never been seen among the numerous teeth of sloths, which 
have been studied by authors, while a genus allied to Mylodon, Sphenodon 
of Lund, presents this character at maturity. Further, the most ex- 
panded portion of these teeth presents considerably smaller dimensions 
than the smallest of the MW. jeffersondi, figured by Leidy ; the diameter of 
the triturating surface is only .66 of that of the same, (Leidy, 1. ¢. xvi, 
fig: .6). 
In the moderate development of the inner bulge, these teeth are like 
some of those of JM. wheatleyt. 
MEGALONYX TORTULUS, Cope, sp. nov. 
Established on two corresponding canine-molars of opposite sides of a 
sloth, found in association with the preceding, These teeth are more dis- 
tinctly curved than in the three species preceding, but are more as in Af. jef- 
fersonti and M. lovodon. Its shaft possesses a peculiarity of the latter, 
which is not seenin WM. wheatley?, M. dissimilis and M. sphenodon, i. e., it 
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