4 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. {NoV. 5, 



three cusps, as in the Stereognathiis ; but the middle pair of cusps 

 in the Hyracotherium are very small, appearing, in fact, as mere 

 conical tubercular elevations of the middle of the ridge connecting 

 the fore part of the base of the outer and inner principal cones. 



In the Hi/ opotamus Rnd Anfhracotherium* y-the intermediate cone 

 between the outer and inner principal cones of the anterior half of 

 the molar tooth is developed to equality of size with them, and three 

 cusps or cones are thus seen on the same transverse line of the crown. 

 But there is no trace of the middle cone or tubercle (like that seen 

 in fig. 5, /, between the outer, o', and inner, p', hinder cones), an- 

 swering to the rudimental cusp in Hyracotherium and to the cone i 

 in Stereognathiis. 



In the little Microtheriimi or Cainotkerium of the miocene de- 

 posits of Germany and France the middle lobe or cone is developed 

 between the pair at the back part of the upper molar, answering to 

 cone i in fig. 5 ; but the cone answering to h, fig. 5, is not developed 

 between the front pair of cones. This tendency, however, to lobes, 

 cones, or cusps, in threes, in the older tertiary Mammals, is very 

 significant evidence, as it seems to me, of the affinities of the small 

 oolitic mammal having the above-described regular sex-cuspid molars. 



The molars of the lower jaw of the Hgopotamiis and other An- 

 thracotherioids show no trace of a lobe or cone intermediate between 

 the outer and inner cones of each transverse pair. The structure of 

 the lower molars of the Hyracotheinum is unknown : it is most pro- 

 bable, however, that the lower molars of the Choeropotamus would 

 most resemble those of the Hyracothere ; and in the penultimate 

 and last grinders of the Chceropotamus a rudimental cusp appears 

 between the outer and inner principal cusps. 



The proportional size, and regularity of form, of the cones of the 

 grinding teeth of the Stereognathiis give a quite different character 

 of the crown from that of the multicuspid molars of the Insectivora, 

 and cause it to resemble more the quadricuspid orpentecuspid molars 

 of the Artiodactyle non -ruminant extinct genera above cited. 



I conclude, therefore, that, like the Dichobunes, Xiphodon, Mi- 

 crotheriuniy Uhagatherium, Hgopotamiis, and Hgracothei'imn, the 

 Stereognathiis ooliticus was a diminutive form of the great Ungu- 

 late order of Mammalia, and that it most probably belonged to the 

 artiodactyle or even-toed division of that order, and to the non-rumi- 

 nant section of that division, the food of w^hich, if we may judge 

 from the existing hogs and peccaries, was of a mixed nature. 



The interest which the above-described fossil from the Stonesfield 

 oolitic slate excites is not exclusively due to its antiquity, its unique- 

 ness, or its peculiarity : much arises out of its relations as a test, in 

 the present state of Palaeontology, of the actual value of a single 

 tooth in the determination of the rest of the organization of an animal, 

 or of so much of it as serves for a recognition of the place of the ex- 

 tinct species in the zoological series : the attempt, at least, to ana- 

 lyse the mental processes by which one aims at the restoration of 



* Quart. Journ. Geol. Soc. vol. iv. pi. 7. figs. 1, G, & 9. 



