1857.] FALCONER MASTODON. 315 



African Elephant, the ridge -formula is also hypisomerous, as in 

 the Stegodons, the ciphers ranging from 7 to 9 in the 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 appearance of elongated wedges, with thinner 

 plates of enamel. For this subgeneric group, the name of Loxodon'^y 

 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 im- 

 portant, 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 ex- 

 pressed (e. g. for the Indian Elephant) by the series 12-|-14-|-18f. 

 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 correspond 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 normally 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 oi EuelephasX, 



[Note. — The following systematic Diagnoses of the genera Mastodon and 

 Elephas were prepared as an Appendix by the author, but their insertion in 

 this place more conveniently elucidates the subject-matter of this memoir. 

 — Edit.] 



* From Xo^os ohliquus, and d^ovs dens, having reference to the rhomb-shaped 

 discs of the worn molars ; an adaptation of the term " Loxodonta " proposed by 

 Fred. Cuvier, ' Hist. Naturelle des Mammiferes,' torn, iii., Article " Elephant 

 d'Afrique." 1835. 



t The illustration in this case is taken from the existing Indian Elephant, E. {Eu- 

 elephas) Indicus, in which the ridge-formula 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 tliroughout 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. 



I From ev bene, and eXe^as, having reference to the typical Elephants most fa- 

 miliarly known. In the illustrations of the ' Fauna Antiqua Sivalensis,' the term 

 Elasmodon was appUed to this subgeneric group : but, the designation of Elasmodus 

 having been preoccupied by Sir Phihp Egerton for a series of fossil fish (Proc. 

 Geol. Soc. vol. iv. p. 163, 1843), to prevent confusion, the term of Euelephas has 

 been substituted for it. 



