OF THE MESOZOIC MAMMALIA. 
191 
relations to the pattern of the molars, canines, incisors and to the shape of the man- 
dible ; in other words to the kind of diet. In order to britrg out these minor char- 
acters clearly, the drawings have been finished with the utmost care and made upon 
a very large scale. ^ A second principle adopted in the drawings is that of composi- 
tion, upon a system which is Mly explained in connection with the text of the plates. 
AVhile open to some objections this has the effect of bringing all the known characters 
of a species which can be legitimately placed together, before the eye at the same 
time. In Professor Owen’s Memoirs, the majority of the specimens thus placed 
together are figured separately. The numbers correspond with those affixed to the 
specimens in the British Museum collection. 
AMPHITHERIUM. 
Since the publication of Professor Owen’s memoir, a portion of a small jaw from 
the Stonesfield Slate has been added to the British Museum collection and referred to 
Amphitherium (No. 36,822). The teeth preserved are the last premolar and five 
molars, in all of which the cro^vns are perfect. A close examination of these crowns, 
in comparison with the figures of A. Prevostii (Mes. Mamm., PL I, fig. 23), and of 
A. Broderipii (PI. I, fig. 25), at first led me to believe that this specimen was wholly 
distinct from Amphitherium, but subsequently these molars were found to correspond 
closely to the somewhat mutilated molar crowns of the type specimen of A. Prevostii, 
as figured in PI. I, figs. 21 and 22. Unfortunately I was unable to compare the ori- 
ginal types, but from a study of all the drawings and descriptions available, this cor- 
respondence has been confirmed, and the conclusion reached that among the speci- 
mens heretofore referred to Amphitlierium, we have the types of three distinct genera. 
The A. Broderipii has, in fact, already been separated with some qualification, by 
Professor Owen,^ under the name AmpMlestes-, the third genus remains to be dis- 
tinguished. 
Let us begin with the type specimen of Amphitlierium,^ the first to be discovered 
and described. All the numerous figures of this specimen which have been published^ 
agree as regards the pattern of the molar crowns. Observe especially m, nij, and m^. 
“ In the fifth molar the middle external cusp is nearly entire to its sharp apex; part 
of the anterior cusp and the base of the internal posterior cusp are preserved.” In 
this description Professor Owen indirectly suggests that the summit of the posterior 
cusp has been broken away. If we adopt this suggestion we must suppose that the 
‘ Palaeontology has suffered much from the mistaken custom of making figures large or small in direct 
proportion to the size of the object illustrated. A quarto plate will often be devoted to some very large object 
in which perhaps the anatomical details are few and simple, while a row of small teeth, full of important 
diagnostic characters, is crowded into such a small scale that it is impossible to make out the details. 
^ Mes. Mamm., p. 16. 
» De Blainville, Comptes Eendus. Aug. 20th, 1838. 
* Prevost. Ann. des Sc. Nat., April, 1825, (PI. 18, fig. 2). Owen, Oeol. Transactions, Ser. 2, Vol. VI., 
1839. Also, Brit. Foss. Mamm., (fig. 16) ; and Mes. Mamm., (figs. 21 and 22). 
