DIliiTVI.INX OF AMERICA. 325 



In the same work* Dr. Le Contc notices a fossil Dicotyles from Benton county, Mis- 

 souri, found in association with bones of tlie Mastodon, for which the name Dicotyles cos- 

 tatua is proposed. 



My friend Le Contc, with his usual liberality, has presented to the Academy of Natural 

 nccs the specimens upon which the species and genera just mentioned have been founded. 

 Of these, I propose to examine in the succeeding pages only the more characteristic; not 

 only for the purpose of determining as far as possible the distinct species and genera they 

 indicate, which alone is a subject of greater importance to Palaeontology than the unrid- 

 dling to which animal every fragment belongs, but more particularly for the sake of com- 

 parison with an almost perfect head of an extinct animal, found in a saltpetre cave in Ken- 

 tucky, belonging to the American Philosophical Society, and deposited by this body, in its 

 desire to advance the interests of Science, in the Cabinet of the Academy of Natural Sci- 

 ences. 



The specimens of Dr. Le Contc's collection are very imperfect, brittle, and mutilated, 

 and their investigation has by no means proved an easy one, nor have the results turned 

 out so satisfactory as are desirable. 



The most characteristic fossil, for which the name Platygonus without doubt must be 

 retained, is tin' fragment of lower jaw presenting the peculiarity from which the animal 

 derives its name. 



The specimen consists of the hinder portion of the right half of the lower jaw of a raid- 

 aged adult. It is much broken, and contains the two posterior molars, also broken, 

 and fragments of the two in advance, (PI. 38, Fig. 3.) Accompanying the specimen, and 

 apparently belonging to the same individual, are. the crowns of the posterior two true mo- 

 ira and premolars of the left side, and the last true molar and the inner lobes of the second, 

 and tin' three premolars of the right side, of the upper jaw. 



The fragment of lower jaw, (PI. :!^. Fig, 3,) is relatively deeper than in Dicotyles, and 

 the angle is not only directed more downwards but it curves very much outwards. (PI. 

 :?. Fig. 9.) The condyle, broken at its inner side, has its articular surface a little more 

 convex than in Dicotyles, and externally is not so prominent, and exhibits a small depres- 

 -lon lor the attachment of the external lateral ligament. The coronoid process is broken 

 away. The fossa posterior to the latter process has the same form as in Dicotyles. but is 

 relatively deeper. 



The two teeth preserved in the specimen (PI. 37, fig. 10,) are considerably worn, the 

 dentine being exposed in lobate patches upon all the dental lobes except the posterior 

 and the internal of the middle pair of the last molar. These teeth are intermediate in 



size to those of (lie two existing -pedes of Dicotyles, and are constructed on the bi • 



type, but then- triturating surfaces have none of the wrinkled appearance existing in Di- 

 cotylea and reaching its excess in Sus, and the principal lobes are more prominently de- 

 veloped and relatively much longer, and the lesser or accessory lobes of Dicotyles disap- 

 pear or exist onlj a- continuous portions of the principal lobe-, from trituration the 

 principal lobes of the teeth m the fossil have become combined mt,, transverse pyramidal 



