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Order PROBOSC1DEA. 
Genus MASTODON. 
Subgenus TETRALOPHODON. 
M. [Tetralophodon] arvernensis (Falconer). — Cuvier, the 
founder of the genus Mastodon, in his work, ‘ Osseraens Fossiles,’ 
tom. i, p. 205, gives as his reason for founding this genus, and 
thereby separating the Mastodons from the true elephants, that the 
molar teeth of Mastodon consisted of a comparatively simple crown 
divided into mammilla}, arranged in transverse ridges more or less 
numerous, and more or less prominent, with corresponding hollows 
between them ; while the molars of the genus Elephas, were much 
more complex, consisting of a far greater number of transverse 
plates, the space between which were filled up with cement. 
Dr. Falconer, one of our greatest authorities on fossil proboscidea, 
divided the genus Mastodon into two subgenera, viz., Trilophodon 
and Tetralophodon, owing to the molar teeth in either of these sub- 
genera having a ternary or quaternary ridged formula. This ridge 
formula enables us to tell with unerring precision the composition 
of the crown of any molar tooth of Mastodon ; the three inter- 
mediate molars shewing invariably the ridge-formula, while the 
tooth in front of these shews one ridge less and the one immediately 
behind shews one ridge more. 
The species Mastodon arvernensis, is the only one, so far as I am 
aware, that is found in Norfolk. The old land surface over-lying 
the chalk and under-lying the Norwich crag is the deposit in which 
the remains of this mammal are found. 
The localities where it has occurred are as follows : — Horstead, 
Thorpe, Bramerton, Postwick, and Whitlingham. 
The chief characteristics of the species are, the multimammillato 
structure of the molars, the absence of tusks in the lower jaw, and 
the valleys between the ridges of the molar teeth being filled up 
with one or more tubercles. 
The species seems to have had a considerable distribution in time, 
as it is also found in an older deposit than that underlying the 
Norwich crag, viz., the Suffolk crag; where it is associated with a 
fauna that shew much warmer climatal conditions than the fauna 
of the old land surface, where the remains have been found in this 
county. It is never found in the forest-bed. 
