458 
THE GEOLOGIST. 
two systems of deposits, and believinfjr that no sufficient reason liad been 
assigned for the absence of the Old Ked fish in Devon and Cornwall, have 
never failed to cherish the belief that, sooner or later, they would be found 
there ; and, indeed, we have heard from time to time that at length the 
wished-for ichthyolites have been exhumed in the southern area. At the 
meeting of the British Association held at Cork, in 1843, Mr. Peach 
brought under the notice of the Geological Section, certain fossils which 
had then recently been found by Mr, Couch, in the Devonian slates, near 
Polperro, in Cornwall. The pala3ontologists to whom they were then sub- 
mitted considered them to be remains of fishes ; and, indeed, the late Mr. 
Hugh Miller subsequently found a specimen amongst them, of which he 
said that "if he had found it in the Old Red Sandstone of Cromarty, he 
would have no hesitation in regarding it as a fragment of some dermal 
plate of A.stcrolepis These fossils were found in great numbers in cer- 
tain localities, and extended along the Cornish coast, at by no means wide 
intervals, from Fowey Harbour to the Kame Head ; they were constantly 
spoken of as the " Polperro fish," and the slates in which they w^ere found 
as the " Polperro fish-beds." At length, Professor M'Coy and Mr. Carter 
of Cambridge subjected them to a rigorous microscopic scrutiny, and pro- 
nounced them to be nothing more than sponges belonging to their new 
genus Steganodictyum, of which they formed two species, S. Cornuhicum 
and 8. Carteri. It may be doubted, however, w^hether certain fossils 
found with them were not true ichthyolites ; indeed, one specimen which, 
a few years since, I found in the Steganodictyum beds at Looe, in Cornwall, 
has been pronounced, by Sir P. Egerton and others, to be a decided ich- 
thyodorulite.* It has not been identified, however, even generically. 
A few weeks since, I had the good fortune to find a fossil in the JPleuro- 
dictyum slates at Meadfoot, near Torquay ; that is, in certainly the lowest 
group of the rocks of South Devon and Corn \a all, and which Sir H. Mur- 
chison has placed on the horizon of the Cephalaspidian and Pterasjpidian 
beds — the lowest of his divisions of the Old Ped of Scotland. From the 
first, I believed it to be a fish-scale or plate ; and very recently, Mr. Davies, 
of the British Museum, has not only confirmed this, but has identified the 
fossil as a scale — or rather, a portion of one — of Phyllolcpis concentricus, 
a fish known only by its fossil scales, and which had hitherto been found 
only in the Clashbennie beds, belonging to Sir R. I. Murchison's Upper 
OldEed. 
This fossil then appears to necessitate the belief, either that the organism 
which it represents had a greater vertical range than has been supposed, — 
that is, that it belonged to the Lower and Middle, as well as Upper Old 
Red fauna, — or that the Pleurodictyuni beds of Devon and Cornwall, in- 
stead of being on the horizon of the Lower, are on that of the Upper Old 
Ped series of Scotland. 
To accept the first of these, apparently the only two alternatives, would 
be to accept the difliculty of supposing that Phyllolepis dates from Cepha- 
laspidian times ; that it witnessed the extmction of this family as w^cll as 
the subsequent introduction and withdrawal of Coccostcus, Asterolcpis, and 
others ; and yet that, unlike its early contemporaries, it failed to leave be- 
hind any trace of its existence in the Old Ped rocks, save only in the 
upper of tlieir three groups. 
Pejecting tliis hypothesis, however, we seem compelled to adopt its rival, 
which amounts to this: — there are in Devon and Cornwall no representa- 
tives of the Lower and Middle Old Ped rocks of Scotland, but the 
lowest — the Pleurodictyum beds — of the former are on the horizon of the 
* See ' Geologist,' vol. iv. pL vi. p. 346. 
