° 
502 
north-east departments of Europe. Thus the ichthyological faunz 
of the old red sandstone has within a few years been found to be 
one of the richest and most prolific kind ; and its extinct species are 
much more curious and remarkable than those of any other forma- 
tion, by their deviation from the conditions of existing genera and 
species. Their most characteristic feature is an immense develop- 
ment of bony matter and enamel on the surface of the skin, thus 
approaching to the external dermal skeleton of Crustacea and In- 
sects. One of these fishes, the Pterichthys, is so largely and almost 
entirely encased with bony plates and scales, that it was at first mis- 
taken for a fossil Water-beetle. 
The nearest analogies we find among modern fishes to the great 
development of bony matter and enamel upon the head and scales 
of many of these ancient species, is that afforded by the large ex- 
ternal bones which form the head and large bony dermal scales 
upon the body of the modern Sturgeons, which further agree with 
- these fossils in having no internal bony skeleton. 
Another analogy occurs in the large external bones of the head 
of the Flying Fish, and of the common Gurnard. These bones are 
also beautifully studded with ornamental tubercles, arranged in 
symmetrical groups like gems and pearls on a jewel. This cha- 
racter is most strongly dominant in the tuberculated bones of the 
fossil genus Coccosteus. The enormous proportion in the size of 
the head to that of the body in the Gurnard, affords another ap- 
proximation to a condition of frequent occurrence in the extinct 
genera of the old red sandstone, and which has given its character- 
istic feature to the genus Cephalaspis. 
Another frequent character in the fossil fishes of the old red sand- 
stone consists in the absence of any internal bony skeleton, as in the 
modern Sturgeons. The large bony dermal scales, first noticed many 
years ago in the old red sandstone of Fife by Dr. Fleming, and then 
referred by him to a fossil Sturgeon, have been confirmed by Prof. 
Agassiz as belonging to a genus nearly allied to the modern Stur- 
geon, and like it possessed a cartilaginous skeleton, of which no 
traces remain in the fossil state. 
Among living fishes, a further analogy to this cartilaginous 
condition of the internal skeleton has recently been found by Pro- 
fessor Owen in the Siren, a fish of equivocal aspect, provided with 
lungs as well as branchiz, and considered as a reptile by preceding 
writers; it lives in the muddy bottoms of the shallow lakes of Seu 
negal, which are periodically dried up, the fish meantime remaining 
immured alive in a kind of cocoon of indurated mud. In the car- 
tilaginous skeleton of this existing Siren from Senegal, the anatomy 
of which has been admirably demonstrated by Professor Owen, we 
find a beautiful analogy to the cartilaginous condition of the skeleton 
of many of the most ancient fossil fishes ; and this analogy explains 
the circumstance of the frequent absence of any remains of an in- 
ternal bony skeleton within the often perfect dermal covering of 
many species of fishes in strata of the older formations. 
From these recent discoveries in Scotland, and the examination of 
