ELEPHANTIDS:. 47 



B. Tetralophodont Group. 



The number of the ridges is usually four in the " intermediate " 

 and five in the last true molars ; but there may be occasionally five 

 in the former and six in the latter. The complete normal ridge- 

 formula is Mm. |=g,M.£Q. 



Mastodon sivalensis, Cautley \ 



The cranium (woodcut, fig. 11) of this specialized species is much 

 vaulted, and the mandibular symphysis short and devoid of incisors. 

 The inner and outer columns of the cheek-teeth are placed alter- 

 nately (although there is some variation in this respect), and when 

 worn present irregularly-shaped disks of dentine. In consequence 

 of this arrangement the valleys are completely blocked, and a small 

 amount of cement is present. In some examples of the " inter- 

 mediate " molars there are five ridges, while there may be six in the 

 last true molar ; the enamel of the milk-molars is vertically grooved 

 but in the true molars it may be either grooved or smooth ; and pre- 

 molars have not been observed. The cheek-teeth are very like 

 those of M . arvernensis ; but the number of accessory tubercles is 

 frequently more numerous, and trefoils are never formed on the 

 columns, while the number of ridges is sometimes greater. The 

 two species are, however, closely allied. 



Hah. India (Siwalik Hills and Punjab). Unless otherwise stated, 

 the following specimens are from the Pliocene of the Siwalik Hills. 



M. 2876. The imperfect cranium of a male, with the mandible in 



(Fig.) apposition. The third true molar is in situ in both jaws 



and is in a half-worn condition. The specimen (woodcut, 



fig. 11) is figured by Falconer and Cautley in the ( Fauna 



Antiqua Sivalensis,' pi. xxxiii. fig. 4. 



Cautley Collection. Presented, 1842. 



M. 2877. The imperfect cranium of a female, showing the half -worn 



(Fig.) m - 3 of either side. Figured by Falconer and Cautley, op. 



cit. pis. xxxii. and xxxiii. figs. 1-3 ; the former figure is 



copied in ' Falconer's Palaeontological Memoirs/ vol. i. 



pi. x. The molar appears to have six ridges. 



Cautley Collection. Presented, 1842. 



1 Journ. As. Soc. Beng. vol. v. p. 294 (1836) ; as a variety of M. angustidens. 



