Miscellaneous. 457 



On Myomorphus cubensis, a new Sabf/enus of Megalonyx. 

 By M. PoMEL. 



The subject of this note is a mandible, almost reduced to its 

 dentarj portion, which was among the objects sent to the French 

 Exhibition of 1867 by M. Pernando de Castro. It was found in 

 some excavations at the baths of Ciego-Montero, and given by 

 Don Jose Figueroa. From the analogy of the matrix, the author 

 associates mth 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 quaternaiy age. 



The mandible has the characters of Megalonyx, 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 ehurnoid. 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 | milli- 

 metre, and becomes gradually thinner on each side. The fourth 

 zone only diff'ers from this in its less hardness and its duUer 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.'ii. 32 



