338 A MEMOIR ON THE EXTINCT 



canines, also, when unworn, are enveloped in enamel, even deeply into the alveoli, except 

 on the posterior concave surface, where a long angular notch extends upwards into the 

 enamel covering. As the animal advances in life, a little after adult age the enamel is 

 completely worn off from the posterior face of the latter tooth, and at a later period the 

 enamelled portion of the tooth becomes completely exserted from the alveolus, the per- 

 manently growing dentinal portion alone occupying the latter. 



In the cave head we have been particularly engaged in examining, the canine teeth do 

 not differ in construction from those of the existing Dicotyles, and their form also is 

 very nearly the same. They are a very little larger than those -of D. torquatus. The 

 superior canine is compressed to about the same degree as in the former, but it is a little 

 narrower, more convex externally, and to a trifling extent less so internally. The lower 

 canine is relatively more exserted than in either existing species of Dicotyles, is convex 

 and smooth internally and externally, and exhibits only a slight disposition to the forma- 

 tion of a ridge at the lower part of the enamelled crown externally. 



As before stated, the incisors are not preserved in the cave head, except one (PI. 37, 

 fig. 19) of those inferior and lateral. This is smaller than in D. torquatus, is enclosed 

 within the alveolus, and appears as if it would have always remained concealed. Its crown 

 is simply mammillary, very slightly compressed antero-internally. 



Having described this interesting specimen in comparison with the two existing species 

 of Dicotyles, we have next to ascertain whether it differs from any of those Dicotylinoe 

 whose former existence has been established by Dr. Le Conte. 



From the fragment of lower jaw of Platygonus compressus the corresponding portion of 

 the cave head differs in its being relatively less deep, and in its angle not being produced 

 so much downwards, and instead of curving outwards, as is so remarkably the case in 

 Platygonus, it is nearly vertical. The post-coronoid depression is also considerably less 

 deep. The posterior two molars are a little larger than those remaining in the specimen 

 of Platygonus, and in the last molar a large accessory lobe is introduced between the fifth 

 and middle pair of lobes, no trace of which exists in the latter. 



A good deal of similarity exists between the fragment of the face of Platygonus and the 

 corresponding portion of the cave head. In both they present about the same degree of 

 lateral compression ; the acute ridge of the superior maxillary bone proceeding from the 

 malar bone, as in Dicotyles, is absent ; the crescentic ridge of the canine alveolus has about 

 the same extent and course; and in the same relative position in advance of the malar 

 bone superiorly the upper maxillary bone is protuberant. Put in the cave head the face 

 is relatively longer, while its intermaxillaries arc broader and very much shorter, being 

 2i inches in length from the lateral notch of the nares, while in Platygonus they are one 

 inch longer. 



The posterior two premolars have nearly the same form, but the basal ridge is less 

 strong in Platygonus, and is not so deeply fovcated. The first premolar in the cave head 

 is quadrate, and has two prominent principal lobes like the two posterior premolars, and 

 possesses a strong basal cingulum open for a short space only internally. In Platygonus 



