Miscellaneous. 457 
On Myomorphus cubensis, a new Subgenus of Megalonyx. 
By M. Pomen. 
The subject of this note is a mandible, almost reduced to its 
dentary portion, which was among the objects sent to the French 
Exhibition of 1867 by M. Fernando de Castro. It was found in 
some excavations at the baths of Ciego-Montero, and given by 
Don José Figueroa. From the analogy of the matrix, the author 
associates with it some plates of tortoises and the posterior part of 
the mandible of a crocodile, probably allied to the alligators. The 
bed is probably of quaternary age. 
The mandible has the characters of Megalonyv, and the same 
dental formula—three teeth in a row, and a fourth isolated in 
front. The molars of the series are prismatic, with a long root, 
slightly arched, the concavity being turned backward; they are 
nearly triangular, with the angles, especially the inner one, blunt 
and rounded. The outer side, which is shortest, is a little depressed 
in the middle; the anterior side is nearly straight, and the pos- 
terior very convex, rounded especially towards the inner angle, 
_ which is the thickest. The first of these teeth has the outer side a 
little oblique; the second is of nearly the same size and form, 
but its outer side is parallel to the alveolar line: the diameters of 
their crowns are as 16:21. The third has its two diameters equal, 
in consequence of the widening of the outer surface; and its postero- 
interior side forms a portion of a cylinder. 
The crown is convex, with anterior and posterior ridges pro- 
duced by two transverse crests of very hard dentine, playing the part 
of enamel. In their minute structure, these teeth show five very dis- 
tinct concentric zones, divisible into two groups of analogous sub- 
stance. The outer zone is a pellicle of very dense substance, traversed 
by a few canals, and shining at its surface like enamel. The second 
zone consists of a substance like ivory, with its transverse fracture 
grained and reticulated by canals ascending obliquely inwards. This 
substance seems to be of the same nature as the outer pellicle, but 
to have more numerous canals and less density. It is the cement 
of many authors; but, unlike the cement of the teeth of the Ungu- 
lata, it has much more analogy with that of the bones, and may be 
named eburnoid. This zone forms the outer slopes of the ridges of 
the crown, where it is about 2 millimetres thick ; it becomes sud- 
denly thin, in order to follow the outer and inner margins. 
The third zone is formed by a very hard dentine, of fibrous 
appearance, but really finely transversely vascular. This forms the 
crests of the coronal ridges, where it shows a thickness of 3 milli- 
metre, and becomes gradually thinner on each side. The fourth 
zone only differs from this in its less hardness and its duller aspect, 
due, no doubt, to a coarser vascularity. It occupies the inner slopes 
of the ridges, and, like the eburnoid substance, which it equals in 
thickness, becomes much attenuated at the inside and outside, until 
it becomes scarcely discernible. In its broader part it seems to 
form fine concentric layers. These two zones constitute the hard 
Ann. & Mag. N. Hist. Ser. 4. Vol. i. oe 
