ngs. I found also a fine
scale of _Holoptychius Nobilissimus_, and a small tooth, bent somewhat
like a nail that had been drawn out of its place by two opposite
wrenches, and from the internal structure of which Professor Owen has
bestowed on the animal to which it belonged the generic name Dendrodus.
I have ascertained, however, through the indispensable assistance of Mr.
George Sanderson, that the genus Holoptychius of Agassiz, named from a
peculiarity in the sculpture of the scale, is the identical genus
Dendrodus of Professor Owen, named from a peculiarity in the structure
of the teeth. Those teeth of the genus Holoptychius, whether of the
Lower or Upper Old Red, that belong to the second or _reptile_ row with
which the creature's jaws were furnished, present in the cross section
the appearance of numerous branches, like those of trees, radiating from
a centre like spokes from the nave of a wheel; and their arborescent
aspect suggested to the Professor the name Dendrodus. It seems truly
wonderful, when one but considers it, to what minute and obscure
ramifications the variety of pattern, specific and generic, which nature
so loves to preserve, is found to descend. We see great diversity of
mode and style in the architecture of a city built of brick; but while
the houses are different, the bricks are always the same. It is not so
in nature. The bricks are as dissimilar as the houses. We find, for
instance, those differences, specific and generic, that obtain among
fishes, both recent and extinct, descending to even the microscopic
structure of their teeth. There is more variety of pattern,--in most
cases of very elegant pattern,--in the sliced fragments of the teeth of
the ichthyolites of a single formation, than in the carved blocks of an
extensive calico-print yard. Each species has its own distinct pattern,
as if in all the individuals of which it consisted the same block had
been employed to stamp it; each genus has its own general _type_ of
pattern, as if the same inventive idea, variously altered and modified,
had been wrought upon in all. In the genus Dendrodus, for instance, it
is the generic type, that from a central nave there should radiate,
spoke-like, a number of leafy branches; but in the several species, the
branches, if I may so express myself, belong to different shrubs, and
present dissimilar outlines. There are no repetitions of earlier
patterns to be found among the generically different ichthyolite