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 

 difi'erent 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 Megcdonyx Jeffersoni. 



The diff'erences of the dental system in this animal and Mega- 

 lonyx are as great as those by which the genera Mylodon, Scelido- 

 therium, and Onathopsis 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 Megalonyoc 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 Tylotherium (Mesotherumi, 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 Myomorphiis ; and the species 

 may be called Megalonyx (or MyomorpJius) cuhensis. The author 

 gives the following measurements as compared with those of Mega- 

 lonyx '. — 



