10 



BRITISH AND EUROPEAN FOSSIL MASTODONS. 



crown ridges of the intermediate molars of the different 

 species. But the colliculi, instead of yielding a gable-shaped 

 or ' tectiform ' section as in the Stegodons, are much more 

 elevated and compressed, so that when the teeth are sawn 

 longitudinally and vertically, the ridges present the appear- 

 ance of elongated wedges, with thinner plates of enamel. For 

 this subgeneric group, the name of Loxodon, 1 first indicated 

 by Frederick Cuvier, has been adopted. It comprises both 

 extinct and living species. 



The last group, which is numerically the largest and most 

 important, including the Elephants with thin-plated molars, 

 as in the existing Asiatic species, is characterized by the 

 ridge-formula being regulated in the ' intermediate molars,' 

 not by hypisomerous ciphers, but by progressive increments 

 (anisomerous) , which may be expressed (e.g. for the Indian 

 Elephant) by the series 12 + 14 + 18. 2 These ciphers, be it 

 remarked, are not put forward as being rigidly exact in every 

 case ; for the higher the numerical expression of the ridge- 

 formula in the species, the more liable to vary within certain 

 limits, dependent on the race, sex, and size of the individual, 

 is the number of the plates ; and they do not rigidly corres- 

 pond throughout in the upper and lower molars, the latter 

 often exhibiting an excess. But it may safely be asserted 

 that the numbers are never transposed or reversed — i.e., the 

 younger tooth among the 'intermediate molars ' never nor- 

 mally exhibits in the same individual a higher number than 

 the older ; the increments may not always be symmetrical, 

 but they are invariably more or less progressive. For this 

 subgeneric group we propose the term of Euelephas. 3 



The following systematic Diagnosis of the genera Mastodon 

 and Elephas was prepared as an Appendix, but its insertion 



the series; but the selected numbers 

 refer only to the ' intermediate molars.' 

 In the species which approach nearest to 

 Loxodon, the numerical expression of 

 the ridge-formula is lower. 



3 From eB bene, and i\4<pas, having 

 reference to the typical Elephants most 

 familiarly known. In the illustrations 

 of the ' Fauna Antiqua Sivalensis,' the 

 term Elasmodon was applied to this sub- 

 generic group ; but, the designation of 

 Elasmodus having been preoccupied by 

 Sir Philip Egerton for a series of fossil 

 fish (Proc. Geol. Soc. vol. iv. p. 163, 1843), 

 to prevent confusion, the term of Euele- 

 phas has been substituted for it. 



1 From Aofis olliquiis, and 6Soi/s dens, 

 having reference to the rhomb-shaped 

 discs of the worn molars; an adapta- 

 tion of the term ' Loxodonta' proposed 

 by Fred. Cuvier ('Hist. Naturelle des 

 Mammiferes,' torn. iii. Article ' Elephant 

 d'Afrique.' 1835). 



2 The illustration in this case is taken 

 from the existing Indian Elephant, E.(Eu- 

 elephas) Indieus, in which the ridge-for- 

 mula of the whole series is nearly thus: — 



Milk molars True molars 



4 + 8 + 12 . 14+18+24 



4 + 8 + 12 " 14 + 18 + 24-27* 



the numerals representing the ridges in 



each tooth, exclusive of the talons. A 



progressive increment runs throughout 



* The ridge-formula for the true molars was subsequently altered to To^t~lt~n~ 



1*t1o t ^4 *- A 7 



See note to description of Elepkas antiquus, and Memoir on E. Columbi. — [Ed]. 



