Prof. Owen—On a New Genus of Mammal. 341 
lobes at the expense of their connecting ridges, the symmetrical 
quadricuspid crown of the Hippopotamus and Anthracothere results. 
By the development of the basal connection between the two outer 
lobes, @ and 6, in Lophiodon, with retention of well-developed 
subtransverse ridges, e, f, the type of the Rhinoceros’s tooth is 
reached. 
The minor or partial modifications which give the characters 
respectively to Paleotherium, Paloplotherium, Hipparion, Equus, 
Hyracotherium, and Pliolophus, in the Perissodactyle series, and to 
Anoplotherium, Hyopotamus, Cheropotamus, Sus, and the Ruminan- 
tia, in the Artiodactyle series, are easily explicable after recognition 
of the modifications by which the leading types of Perissodactyle and 
Ardiodactyle dentitions have diverged from a more generalized un- 
gulate type of grinding surface, such as is shown in the old Eocene 
Hyracotherioids. 
DrEscRIPTION OF PLATE X. 
1. Palatal surface of upper jaw, Miolophus planiceps, nat, size. 
2. — — — Hyracotherium leporinum, nat. size. 
3. Grinding surface of m 2, left side, upper jaw, of Miolophus planiceps, 
macn. 
4, — — — Pliolophus vulpiceps, magn. 
5. — — — Lophiodon medius, nat. size. 
II. On Traces oF GuactaL Drirr In THE SHETLAND IsLAnps. 
By Cuartes W. Pracu, of Wick, N.B. 
aS last summer accepted the kind invitation of Mr. J. 
Gwyn Jeffreys to be his guest on a dredging expedition to 
these Northern Isles, I was induced, by a request from Sir R. I. 
Murchison, to look out for any trace of glacial action that I might 
meet with there. The result of my observations I have thought 
right to lay before the British Association, apologizing for the 
meagre story I have to tell. This poverty arises partly from my 
resolve to devote all time possible to the zoological work, and partly 
from having seen so small a portion of these islands. 
Lerwick.—Our first landing was at Lerwick, where little time 
was spent either then, or when returning. In a short walk that I 
took in the immediate neighbourhood of the town, at the Bay of 
Sclate, I found the sandstone-rocks on the top of the cliff deeply 
rutted, striated, and polished ; and a little inland, on the side of the 
famed Loch of Clickanim, others similarly marked. These mark- 
ings are again to be seen on the opposite side of this bay. The 
ruts, &c., are all in a N. and S. direction, with slight deviations to the 
EK. and W. The direction from which the drift came is evidently 
northerly, and may be traced up the valley, as shown by the wide- 
spread ruin, and the large blocks scattered over it, and resting on 
striated and polished rocks. The hills on each side of this valley, 
and those at the head beyond the docks, bear unmistakeable evi- 
dence also of polishing and grinding. x 
Out Skerries.—After leaving Lerwick, the Out Skerries of Whal- 
sey became our home. The three small islands which form this 
