18 
TEIOTTAET VEETEBRATA OF THE FATtjM. 
also strongly developed as a prominent crest (c.) in front of the inner half of 
the anterior column, from which it is separated by a deep fossa, and there is a trace 
of it on the inner face of the posterior column. On the inner side of the tooth 
tlie enamel ceases just beneath the cingulum, but on the outer and posterior 
sides the enamel-covered surface is greatly deepened, so that in a tooth in which 
the almost unworn posterior column is 11 cm. in height (PI. V. figs. 6 a, 6 b) the 
enamel-covered portion of the crown is only about 3 cm. deep on the inner side, 
while on the outer it is some 8 cm. in depth, and the posterior face of the posterior 
column is covered from base to crown (f 1 cm.). Wear commences at the summit of the 
anterior column, giving rise to a transversely elongated surface. Next the summit 
of the posterior column wears to the same pattern : at this stage the tooth appears as 
Text-fig. 6. 
Semi-diagranimatie figure of the iip])er aud lower teeth of the left side of Arsinoltheriuin aiulreivsi : 
A, upper teeth ; B, lower teetli ; C, outer view of last upper molar. 
«.(•., anterior column of molars ; c., anterior portion of cingulum ; c.’, posterior portion 
of cingulum; posterior column of molars. About j nat. size. 
an extremely hypsodont bilophodont type. Later the wear on the inner side 
reaches the level of the cingulum and the surface resulting from the abrasion of the 
anterior crest of the cingulum joins that of the anterior main column, at first internally 
only, but afterwards externally also, enclosing with it a deep enamel-lined fossa (PI. V. 
fig. 7). At the same time the posterior ])ortion of the cingulum comes into wear : 
its surface is at first continuous with that of the posterior column, but later with the 
anterior also, so that at this stage a continuous inner wall is established and the tooth 
