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one time thought to be scales, but Professor Huxley has shown 
that their appearance is owing to the bloodvessels which 
ramify through the bony disc. By making a horizontal 
section of a portion of the head of the Cephalaspis, and 
placing it under a powerful microscope, we can detect the 
bone- cells or lacunae ; and this of course would have proved 
that these curious heads belonged to vertebrate animals even 
had we never found the bodies (fig. 7). What were the 
food and habits of the Cephalaspis it is hard to say. Some 
persons are inclined to think that the waters which deposited 
the sandstone in which they are found was a great fresh- 
water lake, and that these creatures and those we have yet to 
describe, went creeping about the bottom with their great flat 
heads and staring eyes, sucking in the minute worms and 
animalcules which swarmed there ; for as yet no molluscous 
animals or any remains which would lead us to believe in the 
marine origin of these rocks have been met with in them. 
There are four or five species of Cephalaspis known; the 
commonest is the Cephalaspis Lyelli , which we have just 
described. In the passage beds and uppermost Silurian rocks 
there are the Cephalaspis Murchisoni, C. ornatus, and C. 
Salweyi , which differ but little from the commoner species. 
In Russia, M. Pander has found two species of Cephalaspis, 
which have a beautiful series of symmetrically arranged 
tubercles on the surface of the disc. Although these 
Cephalaspidian fishes appear very quaint in their form and 
proportions when compared with the commoner fish which now 
swim the seas and rivers of Britain, yet if we go to more 
distant regions, we find fish which present many of the 
remarkable characters of the Cephalaspidae. Thus the bony 
pike, or Leyidosteus , of North America, has thick bony scales 
instead of those thin membranous flakes which cover our 
English pike, and the scales of another — the Callidhys — 
resemble still more those of Cephalaspis; whilst in the Canges 
there are several fish the form of whose head is strangely like 
that of the ancient buckler-head. 
But we should now pass on to the next genus of Cephal- 
aspidian fishes — the Auchenaspis. There is only one species 
of Auchenaspis known, the A. Salteri , whose head we have 
represented in fig. 6. It is very much like that of Cephal- 
aspis in shape, but is not nearly so big, being scarcely larger 
than a shilling; whilst, as we should have mentioned before, 
the largest diameter of the cephalic disc of Cephalaspis is 
frequently as much as six or seven inches. The Auchenaspis 
has been separated from the Cephalaspis on account of the 
posterior enlargement of the disc into a sort of neck-plate and 
the absence of a spine. Many palaeontologists are inclined to 
