100
THE ESSEX NATURALIST.
and in the accompanying text-figure. The gap left by cutting
away part of the jaws is marked by a label in Owen's hand-
writing, "Pliolophus vulpiceps." In the back view in the text-
figure the vacant space is marked x. Owen recognised the
close resemblance of this skull to that of Hyracotherium, so far as
comparison could be made, but he thought it belonged to a
distinct genus, Pliolophus,7 because it differs in the less promin-
ence of the intermediate tubercles in the premolar and molar
teeth, and in the less wide interval between the first and second
premolars. It is now, however, generally referred to Hyraco-
therium—often even to the original species, H. leporinum.
Fig i.
Hyracotherium leporinum, Owen (=Pliolophus vulpiceps, Owen) ; hack
view of skull, showing gap (x) left by cutting away jaws of left side, some-
what reduced. London Clay; Harwich. Specimen in the British Museum
(Nat. Hist.)
Far from belonging to the "Hog tribe," Hyracotherium thus
proved to be referable to the odd-toed group of hoofed mammals
which is represented at the present day by the tapir, rhinoceros,
and horse. The typical species would be about as large as a fox,
and the shape of the head appears at first sight much like that
of a fox. As Owen pointed out, however, the greatest expansion
of the brain-case is not behind (as in the flesh-eating mammals),
but in the middle and fore part of the temporal fossa (as in hoofed
vegetable-feeders). The lower jaw and teeth are also those of a
7 R. Owen "Description of a small Lophiodont Mammal (Pliolophus vulpiceps, Owen) from
the London Clay near Harwich," Quart. Journ. Geol. Soc., vol. xiv. (1858), pp. 54-71, pls. ii.-iv.