458 Miscellaneous. 
dentine of odontologists. The fifth zone, forming the axis of the 
tooth and the bottom of the coronal hollow, is the softest of all; it 
is the vascular dentine of authors. Its apparently fibrous structure 
is more loosely vascular than that of the hard dentine; its ascend- 
ing canals become more and more oblique towards the crown. The 
diminution of the four outer zones towards the inner and outer 
margins causes a greater extension of the vascular dentine in these 
directions; and this arrangement explains why the coronal hollow 
opens outwardly. 
These teeth have no rootlets, unless late in life. The part first 
organized seems to be the zone of hardest or enamel-like dentine ; 
but the eburnoid substance seems to be nearly coincident in its 
formation. 
The first tooth is separated from the others by a rather wide 
gap, and thrown nearly to the margin of the mandible, where it 
somewhat resembles a very broad incisor of a rodent; its trans- 
verse section is crescentiform, with the horns blunt and rounded 
off, and the concavity behind. The bone of the mandible is pro- 
duced a very little beyond this tooth, in the form of a very short 
beak, channelled beneath. The two diameters of the tooth are as 
10:22. It has a pellicle of false enamel; but the whole interior of 
the tooth is formed by a compact homogeneous substance, not 
unlike the ivory of the hippopotamus. It shows no trace of vascu- 
larity. An arched line in its middle seems to indicate a band of a 
different and perhaps softer nature. 
The mandibular bone is remarkable for the parallelism of the two 
dental margins and the narrowness of the interval separating them, 
the depth of its ramus beneath the molars, the strong convexity of 
the lower margin beneath this same point, the great extent of the 
symphysis, and the very oblique elevation of the anterior margin 
towards the terminal beak. Except in these and some other details, 
the bone closely resembles its homologue in Megalonya Jeffersoni. 
The differences of the dental system in this animal and Mega- 
lonyx are as great as those by which the genera Mylodon, Scelido- 
therium, and Gnathopsis are distinguished. The serial molars in 
Megalonyx are nearly equal and subquadrangular; in the present 
animal they are rather triangular, and the last is distinctly the 
largest. The isolated tooth in Megalonywx is very oblique, and has 
an elliptical section, whilst in the Cuban fossil it is more arched in 
the direction of its length, and much more like an incisor. This 
character is of great importance, and might seem to be an advance 
towards the dentition of T'ylotherium (Mesotherium, Serr.), if the 
similar tooth in the latter did not appear to be a true incisor. The 
rest of the skeleton will no doubt furnish further characters: for 
the present, the author forms for this animal a new subgeneric sec- 
tion, to which he gives the name of Myomorphus; and the species 
may be called Megalonyx (or Myomorphus) cubensis. The author 
gives the following measurements as compared with those of Mega- 
lonyx :— 
