retained the name o f Megalonyx, and used it in a generic sense, Cuvier offered no
characters whereby other fossil remains might be generically either distinguished
from, or identified with the Megalonyx Jeffersonii, unless, among such remains
there happened to be a tooth, or a claw ex a c tly corresponding with the descriptions
and figures in the Ossemens Fossiles ; and when, o f course, a specific identity, and
not merely a generic relationship would be established.
The greater part o f Cuvier’s chapter on Megalonyx is devoted to the beautiful
and ju stly celebrated reasoning on the ungueal phalanx, whereby it is proved to
belong, not to a gigantic Carnivore o f the Lion-kind, as Jefferson supposed, but
to the le ss formidable order o f Edentate quadrupeds ; and Cuvier, in reference to
the tooth,—the part on which alone a generic character could have been founded,
—merely observes that it resembles at least as much the teeth o f one o f the great
Armadillos, as it does those o f the Sloths.*
In the la st edition o f the Régne Animal, Cuvier introduces the Megatherium
and Megalonyx, between the Sloths and Armadillos ; but alludes to no other
difference between the two genera than that o f size ,—“ l ’autre, le Megalonyx, est
un peu moindre.” (p. 226.) Some systematic naturalists, as Desmarest, and
Fischer, have, therefore, suppressed the genus, and made the Megalonyx a spe cie s
o f Megatherixmi under the name of Megatherium Jeffersonii. The den-tal characters
o f the genus Megatherium are laid down by Fischei’t as fo llow s :—“ D ent,
p rim , et Ian. g. molares | - | , obducti, tritores, corónide nunc plana transversim sulcatá
nunc medio excavatá marginibus promiimlis.'’ That Megalonyx had the same number
o f molares as Megatherium, (supposing that number in the Megathere to be correctly
stated, which it is not,) is here assumed from analogy, for neither Jefferson,
Wistar, nor Cuvier, — the authorities for Megalonyx quoted by Fischer —
p ossessed other means o f knowing the dentition o f that animal than were afforded
b y the fragment o f a sing le tooth.
Now the almost entire lower jaw about to be described offers, in so far as
respects the general form and structure o f the teeth, the same kind and degree o f
correspondence with the Megatherium, as does the Megalonyx Jeffersonii o f ?
Cuvier : and, what is only probable in that spe cie s, is here certain, viz., an agreement
with the Megatherium in the class, viz. molares, to which the teeth exclus
iv ely belong. The question, therefore, on which I find myself, in the outset,
called upon to come to a decision is, as to the preference o f the mode o f viewing
the subject o f the generic relationship o f the Megalonyx adopted by .Desmarest,
Fischer, &c., or o f that, on which Cuvier, and after him Dr. Harlan, have practica
lly acted : whether, in short, the genus Megatherium is to rest upon the more
• Speaking of this tootli, Cuvier observes, “ J e l ’avoiscru d'abord nécessairement de paresseux; maisaujourd-
hui que je connois mieux Tostéologie des divers tatous, je trouve qu’elle ressemble au moins autant à une dent de
l’un des grands tatous.—Loc. cit. p. 172.
t Synopsis Mammalium.
comprehensive characters o f kind and general structure o f the teeth, or upon the
more restricted ones, o f form and such modifications in the disposition and proportions
o f the component textures o f the tootli, as give rise to the characteristic
appearances o f the triturating surface o f the crown.
With respect to ex isting Mammalia, most naturalists o f the present day
seem to be unanimous as to the convenience at lea st of founding a generic or sub generic
distinction on well marked modifications in the form and structure o f the
teeth, although they may correspond in number and kind, in proof o f which it
needs only to peruse the pages o f a Systema Mammalium which relate to the
distribution o f the Rodent Order. According to this mode o f viewing the
logical abstractions under which spe cie s are grouped together, the extinct
Edentate Mammal discovered by Jefferson must be referred to a genus distinct
from Megatherium, and for which the term Megalonyx should be retained.
Th is will be sufficiently evident by comparing the descriptions given b y Cuvier
o f one o f the teeth o f the Megalonyx Jeffersonii, and b y Dr. Harlan o f a tooth o f
his Megalonyx laqueatus, with those o f the Megatherium which have been published
by Mr. Clift. The fragment o f the molar tooth o f the Megalonyx Jeffersonii, described
and figured in the Ossemens Fossiles, seems to have been implanted in the
jaw, lik e the teeth o f the Megatherium, b y a simple hollow b a se similar in form and
siz e to the protruded crown : its structure Cuvier describes as consisting o f a
central cylinder o f bone enveloped in a sheath o f enamel.* The transverse section
o f this tooth presents an irregular elliptical form, the external contour being
gently and uniformly convex, the internal one, undulating; convex in the middle,
and sligh tly concave on each side, arising from the tootli being traversed longitudinally
on its inner side by two wide and shallow depressions.
The imperfect tooth o f the spe cie s called by Dr. Harlan Megalonyx
laqueatus, and o f which a ca st was presented b y that able and industrious
naturalist to the Museum o f the Royal College o f Surgeons, resembles in general
form, and especia lly in the characteristic double longitudinal groove on the inner
side, the tooth o f the Megalonyx Jeffersonii. I t is thus described by Dr. Harlan:
“ The fractured molar tooth appears to have belonged to the inferior maxilla
on the right side ; the crown is d e stro y ed ; a part o f the cavity o f the root remains.
The body is compressed transversely, and presents a double curvature, which renders
its anterior and exterior aspects slightly con v ex ; the posterior and interior
gently concave ; these surfaces are all uniform, with the exception o f the interior
or mesial aspect, which presents a longitudinal rib or ridge, one-half the thickness
o f the long diameter o f the to o th ; with a broad, not profound longitudinal
* I t is most probable that the substance which is here termed “ enamel,” is similar to that which forms the
dense prominent ridges in the tooth of the Megatherium, and which I have shown to be composed of minute
parallel calcigcrous tubes, similar to the ivory or bone of the human tooth.