SYSTEM OF NATURE. 
67 
skeletons, like those of Mammalia, birds and reptiles, are 
composed chiefly of a calcareous earth, pervading an or¬ 
ganic base: hence the durability of their remains. In 
the cartilaginous series, on the contrary, the skeleton con¬ 
tains scarce any of this earth : it is a framework of indu¬ 
rated animal matter, elastic, semitransparent, yielding 
easily to the knife, and, like all mere animal substances, 
inevitably subject to decay. I have seen the huge carti¬ 
laginous skeleton of a shark lost in a mass of putrefaction 
in less than a fortnight. I have found the minutest bones 
of the osseous ichthyolites of the lias entire after the lapse 
of unnumbered centuries.”* 
These views are still further corroborated by the most 
learned and eminent of all ichthyologists, Lacepede, in 
whose works we find not simply a tacit assent to the fact 
that there exist two separate and distinct groups of fish, 
but great pains taken to show that each contains represen¬ 
tatives of the other, and, as though in anticipation, the si¬ 
milarities existing between the two groups pointed out, 
and a table of these similarities or parallels drawn up in 
a double series, as under. 
CARTILAGINOUS. 
OSSEOUS. 
Petromyzon = 
Muraena 
Raia = 
Pleuronectes 
Squalus = 
Esox 
Accipenser = 
Loricaria 
Syngnathus = 
Fistularia 
Pegasus =• 
Trigla 
Torpedo = 
Gymnotus. 
* The Old Red Sandstone, 
hy Hugh Miller, 
F 2 
