OF THE MESOZOIC MAMMALIA. 
193 
P)-evostii of the Buckland Collection (Mes. Mamm., fig. 23); also how the latter differ 
from those of Amphilestes. It is clear that the two fossils, last named, resemble each 
other much more closely than they do Arnphitherium, and in the discrepancy which 
exists between the figures and descriptions of the A. Prevostii under discussion, it is 
difficult to know what to accept and what to reject. All the available figures repre- 
sent the molars of this specimen as follows; they have compactly placed crowns, 
narrow at the base and bearing three cusps, the median cusp slightly the largest ; 
there is perhaps a trace of an internal cingulum appearing upon the anterior and pos- 
terior slope, but it does not overlap the base sufficiently to separate the crowns as in 
Amphilestes. The crowns are described by Professor Owen as quinquecuspidate, 
(Mes. Mamm., p. 14) and the formula is given I 3 C 1 pm. 6 m. 6. Mr. Lydekker 
gives the formula as follows^ : I 4 C I pm. 4 in. 7. This is probably correct. 
AMPHILESTES, Plate VIII, fig. 1. 
The fourth specimen of AmpMtJieriim was originally designated by Pro- 
fessor OweiP as A. Broderipii, but in his subsequent memoir, he tentatively pro- 
posed the name Amphilestes^ which is undoubtedly valid, as distinguished from the 
type of Amphitherium, the only doubt being whether the genus may not embrace Am- 
phitylus. This genus also has but four premolars.^ The molar crowns, as viewed on 
the inner surface, are well separated from each other by the fore and aft extension of 
the basal cingula. “ Each molar presents a large middle cusp, with a smaller but 
well developed and pointed cusp at the fore and back part of its base ; the ‘ cingulum,’ 
a part peculiar to mammalian teeth, plainly traverses the inner side of the crown, 
Avhere it develops three small cusps, one at the base of the large external cusp, and 
the other two forming the anterior and posterior extremities of the tooth.” (p. 16, 
Mes. Mamm.). These molars approach those of Phascolotherium in pattern. So far 
as preserved, the contour of the ramus of Amphilestes resembles that of Amphitherium. 
In both genera the coronoid is broad and rather low, and the condyle is on a level 
Avith or slightly below the molars. In Amphitylus, on the other hand, the condyle is 
pedunculate and considerably raised above the molar level, while the coronoid is 
narrower than in the above genus. 
The three genera may be clearly distinguished as follows ; 
Amphitherium. 
Type. A. Prevostii, De Bl. ? pms j 
m 5 
Molars bicuspidate, with a pos- 
terior heel : no cingulum between 
the molars ; an internal cingulum ; 
condyle on the molar level. 
Amphitylus. 
Type, A. Prevostii, Owen, i j c ^ pm 
jm- 
Molars tricuspidate, compactly 
placed; cingulum faint or wanting 
between the molars ; condyle ele- 
vated and pedunculate. 
Amphilestes. 
Type, A. BroderipU, Owen, i j c i 
pm jm^ 
Molars tricuspidate, separate, 
cingulum strong forming anterior 
and posterior basal cusps ; condyle 
on the molar level. 
* In a letter to me dated April 16th, 1887. See fig. 2a, Amphitylus upon a later page. 
^ Geol. Transactions, 2nd Series. Vol. VI, pi. 6, fig. 1. 
’ Mr. Lydekker (April 16th,) sends me the following formula ; I 4 C 1 pm. 4 M 7. 
