OSTEOLOGY OE THE HYOPOTAMIDAh 
87 
and I must state that I have not seen a single specimen belonging to the clidactyle 
Diplopus from Hempstead, and, vice versa, not a single specimen of the tetradactyle 
Hyopotamus from Hordwell. The state of preservation of the fossils in both deposits 
is very different, and, as far as I can judge from information received in the 
British Museum, the tetradactyle genus Hyopotamus , identical with the genus from 
Buy, seems to be confined to Hempstead, while the didactyle form is found only at 
Hordwell *. I hope, however, to discuss the stratigraphical questions more fully at the 
end of my paper. 
The two middle metatarsals of Diplopus, seemingly from the same individual, with 
three tarsal bones, are figured of the natural size in Plate XXXVIII. figs. 3 & 4, and 
two others, from a larger individual, Plate XXXV. fig. 5. The three phalanges of the 
fourth digit are a restoration, as I had only the corresponding phalanges from the other 
side ; the two metatarsals are also from different individuals, and the third is a little 
smaller than the fourth. 
The difference of these two middle digits of the pes from the corresponding bones of 
Hyopotamus is very great in general shape, section, and in some of the minor relations 
to the tarsal bones, the principal relations being the same in both genera. 
The dissimilarity in shape is of the same order as that noticed in reference to the meta- 
carpals. Instead of the flattened and angular metatarsals of Hyopotamus as seen in 
section Plate XXXVIII. fig. 1, we have, in Diplopus, very rounded, mutually symme- 
trical digits, which adapt themselves mutually by a large, flat inner side, and are sym- 
metrically rounded both in and outside, so as to present in section nearly a perfect half 
cylinder (Plate XXXVIII. v., figs. 3, 4, 5). By this shape they differ much from the middle 
digits of the equally didactyle Anoplotherium and Anthracotherium magnum (the digits 
of which I have from Bochette, Lausanne), but present a resemblance to the same bones 
of the Xiphodon and Entelodon (didactyle), and also to that of the common Hog, as this 
last may be said to be practically didactyle. As seen in Plate XXXV. fig. 5 the distal 
ends are considerably broadened, and the articular ridge, though confined to the palmar 
side of the distal extremity, is prolonged in the form of a very low, but visible, elevation 
along the lower end to the anterior surface of the distal articulation (see Plate XXXVIII. 
fig. 6, and Plate XXXV. fig. 5). These slight peculiarities, which are too numerous 
to be all noticed, clearly indicate a somewhat better adaptation to didactyle locomotion, 
or at least some nearer approach to our recent didactyle forms than is exhibited by older 
forms, such as Anoplotherium — every new experiment of nature to produce a didactyle 
genus seeming to be more successful than the preceding one. However, I have no doubt 
the experiment ended there; and no direct connexion exists between the didactyle 
* I have seen a very large lunare from Hempstead, which appears to indicate the presence of a larger 
Hyopotamus in this deposit ; a very large cuboid from the same locality, though much rolled, seems to indi- 
cate, so far as can he judged by its imperfect state, the presence of another very large tetradactyle species at 
Hempstead. The cuboid iu question presented on its distal surface two facets for the fourth and fifth digits, 
and no beak- like posterior projection. 
