necessary office during the Tertiary period,
which is allotted to them in the present ocean.
We have further evidence to shew, that in
times anterior to, and during the deposition of
the Chalk, the same important functions were
consigned to other carnivorous Mollusks, viz.
the Testaceous Cephalopods ;* these are of comparatively
rare occurrence in the Tertiary strata,
and in our modern seas; but, throughout the
Secondary and Transition formations, where carnivorous
Trachelipods are either wholly wanting,
or extremely scarce, we find abundant remains
of carnivorous Cephalopods, consisting of the
chambered shells of Nautili and Ammonites,
and many kindred extinct genera of polytha-
lamous shells of extraordinary beauty. The
Molluscous inhabitants of all these chambered
shells, probably possessed the voracious habits
of the modern Cuttle Fish, and by feeding
like them upon young Testacea and Crustacea,
restricted the excessive increase of animal life
at the bottom of the more ancient seas. Their
sudden and nearly total disappearance at the
commencement of the Tertiary era, would have
caused a blank in the “ police of nature,”
allowing the herbivorous tribes\to increase to an
excess, that would ultimately have been destructive
of marine vegetation, as well as of
themselves, had they not been replaced by a
* See explanation of the term Cephalopod, in note at p. 303.
different order of carnivorous creatures, destined
to perform in another manner, the office which
the inhabitants of Ammonites and various extinct
genera of chambered shells then ceased to discharge.
From that time onwards, we have evidence
of the abundance of carnivorous Trachelipods,
and we see good reason to adopt the
conclusion of Mr. Dillwyn, that “ in the formations
above the Chalk, the vast and sudden
decrease of one predaceous tribe has been provided
for by the creation of many new genera,
and species, possessed of similar appetencies, and
yet formed for obtaining their prey by habits entirely
different from those of the Cephalopods.”*
The design of the Creator seems at all times
to have been, to fill the waters of the seas,
and cover the surface of the earth with the
greatest possible amount of organized beings
enjoying life ; and the same expedient of adapting
the vegetable kingdom to become the basis of the
life of animals, and of multiplying largely the
amount of animal existence by the addition of
Carnivora to the Herbivora, appears to have
prevailed from the first commencement of organic
life unto the present hour.*
* Mr. Dillwyn observes further, that all the herbivorous marine
Trachelipods of the Transition and Secondary strata were furnished
with an operculum, as if to protect them against the
carnivorous Cephalopods which then prevailed abundantly; but
that in the Tertiary formations, numerous herbivorous genera
appear, which are not furnished with opercula, as if no longer
requiring the protection of such a shield, after the extinction