154 THE MAMMALIA OF THE DEEP EIVEK BEDS. 



is similar, except that the inner ridge is more prominent and encloses a shallow pos- 

 terior fossette. The fourth premolar has all the elements of a molar, though owing 

 to the small size of some of these elements it cannot be called exactly molariform. 

 The protoconid is crescentic and there is a small paraconid ; the postero-external 

 crescent is formed by the metaconid, which is low and obscurely separated from the 

 protoconid ; the deuteroconid is very clearly demarcated from the protoconid and a 

 low tetartoconid completely encloses the posterior valley or fossette, while the ante- 

 rior valley still opens internally between the para- and deuteroconids. The molars 

 are high and elongate from before backward, and increase in size from m. 1 to m. 3 ; 

 the cingulum is developed only on the front and rear faces of the crown, and a tuber- 

 cle between the external crescents represents the mesostylid. The talon of in. s is 

 large and consists of two crescents separated by a narrow valley. 



The only specimen of a cranial cast in the collection which can be referred to 

 Merycocftcerus is not in a satisfactory state of preservation and displays but little 

 that is characteristic. Compared with the brain-cast of Mesoreodon, it exhibits sim- 

 ilar differences to those which are to be observed between larger and smaller species 

 of existing artiodactyls. The hemispheres are broader and of more uniform width, 

 tapering less anteriorly; the convolutions are but obscurely marked in the specimen 

 and can be interpreted only with difficulty, but the sulci appear to be more sinuous 

 and the accessory sulci somewhat better developed than in Mesoreodon. The anterior 

 portion of the hemispheres is of greater vertical depth proportionately, while the 

 temporo-sphenoidal lobe is relatively rather smaller. The medulla oblongata is large 

 and of subcircular section. The cerebellum is too much damaged for accurate de- 

 scription, but it appears to be rather high and narrow. 



The atlas is broad, short antero-posteriorly and of robust construction. The 

 anterior cotyli are large both vertically and transversely ; the two surfaces are almost 

 in contact below, but above are separated by a wide triangular notch which emargin- 

 ates the neural arch. The neural canal is relatively small, especially its anterior 

 opening. The sides of the neural arch are steeply inclined and end above in a mas- 

 sive tubercle, which forms a spine of unusual height. The articular surfaces for the 

 centrum of the axis form an angle of about 45° with the median line ; in shape they 

 are low and wide and their medial edges are reflected upon the sides of the neural 

 canal to form the very large continuous facet for the odontoid process. The inferior 

 arch is strongly convex from side to side and displays a small hypapophysial tubercle 

 near the hinder margin. The transverse process extends well forward and has con- 

 verted the atlanteo-diapophysial notch into a foramen. The process is not much ex- 

 tended transversely but widens posteriorly ; its course on the side of the vertebra is 



