232 Geuhgical Sxxnety : — 



formations and localities where they are elsewhere met with in Europe. 

 The Mastodon of the Crag forms the subject of this first part of the 

 memoir : the second part will treat of the Elephant-remains found 

 in Britain. The author commenced by insisting on the importance 

 to geology that every mammal found in the fossil state should be 

 defined as reg.rds, first, its s])ecific distinctness; and, secondlJ^ its 

 range of existence geographically and in time, with as much severe 

 exactitude as the available materials and the state of our knowledge 

 will admit. He observed that with regard to the remains of the 

 proboscidean genera, Dinotherium, Mastodon, and Elephant, some of 

 which abound in the miocene and j)liocene deposits of Europe, Asia, 

 and America, the opinions respecting the species and their nomen- 

 clature, in all the standard palaeontological works on the subject, are 

 extremely unsettled and often contradictory. 



Dr. Falconer then proceeded to explain his views of the natural 

 classification of the proboscidean Pachyderraaia, recent and fossil, 

 according to dental characters. In the Dinothere, with its tapiroid 

 molars, the last milk-molar and the antepenultimate (or first) true 

 molar are invariably characterized by a "ternary-ridged-crown- 

 formula," or in other words, their crowns are divided into three trans- 

 verse ridges. In the Mastodon not only the last milk-molar and 

 the first true molar, but also the second or penultimate true molar 

 (being three teeth in immediate contiguity), are invariably charac- 

 terized in both jaws by an isomerous division of the crown into either 

 three or four ridges ; or, in other words, are severally characterized 

 by either a "ternary-" or " quatemary-ridge-formula." I'hese 

 three isomerous-ridged teeth are referred to as " the intermediate 

 molars." To the ternary-ridged species the author assigns the sub- 

 generic name of Trilophodon ; and Tetralophodon, to the quaternary- 

 ridged species. The molar in front, and that one behind these in- 

 termediate molars are also characteristically modified in these two 

 suberenera. In Trilophodon the penultimate or second milk-molar 

 is two-ridged and the last true molar isft)ur-ridged : in Tetralophodon 

 the former is three-ridged, and the latter five-ridged. The author 

 considers it highlv probable that a subgeneric group characterized 

 bv a quinary-ridge-formula (^Pentelophodon) has existed in nature, 

 but of which no remains have yet been discovered. 



The Elephants are distinguished from the Mastodons by the absence 

 of an isomerous-ridge-formula, as regards the three intermediate 

 molars, and bv the ridges ranging from six up to an indefinite 

 number in these teeth, in difi^erent groups of species. Dr. Falconer 

 arranges the numerous fossil and recent forms in three natural sub- 

 genera, founded on the ridge-formula, in conjunction with other 

 characters. In the Stcgodon (comprising besides other forms the 

 Mastodon elephantoides, Clift) the ridge-formula is hypisomerous ; 

 and the ridges number six or eight. The Loxodon (including the 

 African Elephant) is also hypisomerous, and has from seven to nine 

 plates cr ridges. The Euelephas (including the Elephas indicus 

 and six fossil speci-^s) is the largest and most important group, 

 and comprises the typical Elephants having thin-plated molars. 



