844 ON THE EXTINCT MAMMALIA OF 



animal, and closely approaches it in constitution, form, and size. It appears to have 

 been about one-fourth worn, and was furnished with a pair of short fangs. The crown 

 is six and a half lines long antero-internally, and four and a half lines antero-exter- 

 nally. It curves backward and outward to about the same extent as in the Crested 

 Porcupine, and, as in this, presents a pair of lateral enamel folds dividing the crown 

 into two portions. The triturating surface measures four lines and a quarter antero- 

 posteriorly, and three and a quarter transversely at the anterior division of the crown. 

 At the base of the latter it measures four lines transversely. The anterior division of 

 the triturating surface exhibits a transverse bow-like islet, and the posterior a trans- 

 verse boot-shaped islet, together with a minute circular one. 



The second specimen consisted of the crown of an unworn tooth, which presents 

 less resemblance to any of the teeth of the Crested Porcupine than the former, and 

 may perhaps belong to a different animal from it. 



Compared with the left upper molars of the Crested Porcupine, which it most re- 

 sembles, it is more square in transverse section, or its antero-posterior diameter is 

 proportionately less. The outer and posterior surfaces form vertical planes, the ante- 

 rior surface is convex, and the inner one alone forms an enamel fold penetrating the 

 crown. A section of the specimen near the triturating surface, as represented in 

 figure 24, magnified one and a half diameters, exhibits three transverse, elongated, 

 elliptical enamel islets, with the internal transverse valley projecting between the 

 inner ends of the anterior pair of islets. 



The length of the specimen, before a section was made, was nearly half an inch 

 anteriorly. Its antero-posterior diameter is three linesj its transverse diameter three 

 lines and a half. 



