86 BRITISH AND EUROPEAN FOSSIL ELEPHANTS. 



valleys. In some sections as many as eleven distinct strata of 

 this substance may be counted. 1 But the ciphers yielded by 

 the ' ridge-formula ' place the species in close affinity with the 

 Loxodons, and more particularly with the species named E. 

 (Lox.) planifrons. Remains of E. {Steg.) insignis have been 

 discovered in immense abundance in the Sewalik hills, and 

 specimens illustrative of the dentition of every age and in 

 every stage of wear are contained in the great Indian col- 

 lection of the British Museum. The rigid constancy in the 

 number of ridges observable in the two subgenera of Mastodon 

 is no longer maintained. As stated in the preceding part of 

 this paper, the higher the numerical expression of the ' ridge- 

 fbrmula ' in the species, the more liable is the number of 

 ridges to vary within certain limits dependent on the race, 

 sex, and size of the individual ; and the molars of the lower 

 jaw often exhibit an excess. After examining a very large 

 number of specimens of all ages, the prevailing numerical 

 expression of the ridge-formula, exclusive of ' talons,' in E. 

 (Stegodon) insignis has appeared to me to be thus : — 



Milk molars. True molars. 



2 + 5 + 7 : 7+ 8 +(10-11 ). • 



2 + 5 + 7: 7+(8-9) + (ll-13). 



I have already remarked that all the known species of 

 Stegodon belong to that species of the Proboscideans in which 

 the ridges are transverse, and the valleys open. It may be 

 expected, without much temerity, that other species remain 

 to be discovered in the fossil state, in which the mammillse will 

 be disposed more or less alternately, with outlying tubercles 

 and interrupted valleys, as in the ' Stenocoronine ' type. 



IT. — Pentalophodon. 



Prom the circumstance that so many Mastodons present 

 the ciphers either 3 or 4 constantly in the ridges of the inter- 

 mediate molars of two groups of species, and that in the next 

 allied group, Stegodon, Elephas (Stegodon) Cliftii in like 

 manner presents the cipher 6 in two of the same teeth, while 

 the prevailing number augments in E. (Stegodon) bombifrons 

 and E. Stegodon insignis, with faith in the harmony of nature 

 it might have been with some confidence anticipated that 

 another Proboscidean type remained to be discovered in the 

 fossil state, intermediate between Tetralophodon and Stegodon, 

 in which a quinary ridge-formula would be presented, consti- 

 tuting a third subdivision of the genus Mastodon, to which 

 the name of Pentalophodon would be applicable. 



It appears to me that the Indian fossil species M. (Tetralo- 



1 Fauna Antiqua Sivalensis, PI. vi. fig. 7. 



