Figure 1. Trimerus Delphinocephalus.
2. Calymene Diops.
3. Asaphus Micrurus.
4. Cryptolithus Tessellatus.
5. Paradoxides Boltoni.
6. Triarthrus Beckii.
7. Isotelus Cyclops.
8. Dipleura Dekayi.
9. Head of D. Dekayi.
10. Ceraurus Pleurexanthemus.
The above figures represented on the Frontispiece to this volume, were
first published in the Monthly Journal of Geology, &c. for June, 1832,
and I am indebted to C. A. Poulson, Esq., for the use of them in this
Monograph.
INTRODUCTION.
—————
Some geologists imagine that the order of creation is registered in
the rocks which compose the external crust of the earth, and that they
can there clearly read a progressive development of organic life; in
other words, that a succession of more perfect animals may be traced in
ascending from the lower strata to the upper or more recent formations;
that there is a gradual approach to the present system of things, and
a succession of destructions and creations; worlds of living beings
alternating with worlds of desolation and death, antecedent to the
existence of man.
Others, again, contend that there is often a wide and palpable
discrepancy between the nature of the rock, and the fossils which it
contains, and, therefore, that such inquiries afford no clue, whatever,
to the order of creation.[1] We propose not to enter the field of
controversy. Fossils are undoubtedly historic medallions of remote
periods in the natural history of our earth, and our design is, merely
to illustrate with them a neglected department of ancient zoology, by
describing a few which have recently fallen under our own observation.
[Footnote 1: Nothing can be more opposed to true science, than to
pronounce on the priority of formation, or the comparative age of
rocks, from either their structure, or the organic remains they
present. M. Alexandre Brongniart thus propounds his opinion: "In those
cases where characters derived from the nature of the rocks are opposed
to those which we derive from organic remains, I should give the
preponderance to the latter." This seems to us to imply an admission,
that nothing definite can be inferred from the _nature of the rocks_;
moreover, that between the nature of the rock, and the organic remains,
there may be a palpable discrepancy; and that these may be even at
complete antipodes with each other. The event has proved, from what we
have already mentioned, that no evidence as to priority can be obtained
from the nature of the fossil remains displayed in particular strata.
In addition to what has been said on this subject, we may further
state, that _encrinites_, _entrochites_, and _pentacrinites_ are found
in clay slate, grauwacke, transition limestone, alpine limestone,
lias, muschelkalk, and chalk. It may be reasonably asked how these
three species of fossils could indicate any particular formation, when
they are found in so many types and structures of rocks altogether
different? If they would go to prove any thing at all, it would be that
of a _contemporaneous_ formation; but certainly not distinct epochas.
_See Eclectic Review, July, 1832._]
In some varieties of rocks there is often found the fossil remains of
an animal which bears some resemblance to certain species of the crab.
The back of this organic relic is commonly divided by two deep grooves
or furrows, into three longitudinal lobes, and from this circumstance,
the term _Trilobite_ has been applied as a family name to distinguish
this whole race of beings. This general appellation, however, though in
most of the species, highly appropriate, is by no means applicable to
all.
The individuals which compose the family of the trilobites resemble
each other in many important particulars, and form together an
exceedingly natural group. The body, with but few exceptions, is
divided transversely into three parts. The anterior portion or head
often resembles the buckler of the _horse foot_ or _king crab_
(_limulus polyphemus_), so common on our sea coast. The middle portion
is the _abdomen_, and is always separated transversely into a number
of segments or articulations, generally diminishing in breadth as they
recede from the head. The posterior end is the _tail_, which, though
in some species, a mere prolongation of the abdomen, that can scarcely
be distinguished from it, yet in others it assumes a genuine caudal
appendage.
The head of the trilobite is also generally divided into three parts:
the middle is called the _front_, or forehead; and the lateral portions
the _cheeks_. In most cases, a projecting tubercle, or knob, is
observable on the anterior surface of each cheek, which has much the
appearance of an eye. Its reticulated structure is in many instances so
analogous to that of the eyes of some crustaceous animals, and also of
some species of insects, that there can be but little doubt that these
tubercular projections, were true organs of vision.
Some of the genera which belong to this remarkable race of fossil
animals, possessed the power of rolling or coiling themselves up into a
kind of ball, like certain species of insects, or like the armadillo;
and they are always found embedded in the rocks in this attitude.
Such are the general characters by which these petrifactions may be
known, and they will be found illustrated in a manner more or less
striking, in most of the species. The exceptions, which rarely occur,
will be distinctly marked, when the species are described.
The superior covering, or upper shell of the trilobite is the only part
of the animal, concerning which we have any satisfactory knowledge.
It is conjectured that it was furnished with articulated feet, but no
traces of any organs of progressive motion have hitherto been fairly
discovered.[2] Hence, it may be reasonably supposed, that the structure
of the lower portions of the animal were so soft and delicate, as to
render them incapable of sustaining the process of mineralization,
which the hard crustaceous covering of the back so successfully
undergoes.
[Footnote 2: Mr. Parkinson states, that in a trilobite which he
possessed he thought he perceived the _points_ of the feet; but on
endeavouring to detach the piece of rock in which it was embedded, the
specimen was entirely shivered, though he worked at it with the utmost
care. A portion of the underside of a trilobite (_Isotelus gigas_)
near the anterior edge of the head, was distinctly ascertained, by Dr.
Dekay, but only enough to convince him of its analogy in this part with
that of the limulus polyphemus no organs of locomotion could be seen.
Mr. Stokes, the distinguished fossilist of London, has confirmed the
observation of Dr. Dekay, by some dissections of his own.]
That these petrifactions were once marine animals there can be little
doubt, for they are always found associated in the same rocks with
shells, and other productions peculiar to the sea.
The Trilobite is supposed by many naturalists to be one of the first
animated beings of our earth called into existence by the great Author
of nature.[3] It was first noticed more than two centuries ago, among
the petrifactions which abound in a calcareous rock, at Dudley, in
England, and was from this circumstance, called for a long time, the
_Dudley fossil_. Linné gave it the name of the _Paradoxical insect_;
but whether an insect, a crustaceous animal, or a shell, is still
considered by many as problematical.
[Footnote 3: It is obvious, that if most of the gelatinous animals
which now inhabit our seas, were to become extinct, few or no traces
of them could be found in any succeeding depositions of earthy matter.
Whatever kind of animal life, therefore, may have been the first which
appeared in our planet, must be entirely hypothetical. All that we
can with certainty say of it, is, that it was best adapted to the
circumstances, in which it was to exist, and that it was consistent
with the wisdom and design which we see every where pervading the
universe.]
Notwithstanding the high antiquity of the family of the Trilobites,
and the remarkable characters the different individuals which compose
it, sustain in the animal kingdom; till within a very few years, the
whole race has been almost entirely neglected by naturalists. The
first attempt at any systematic arrangement of the genera and species,
was made in 1815, by Alexander Brongniart, Professor of Mineralogy,
&c. &c., in Paris.[4] Until that period, the term _Entomolithus
Paradoxus_, proposed by Linné, was applied to all the fossil remains,
which in their general appearance bore any resemblance to that found at
Dudley, and which he first described under that name. The confusion,
therefore, which existed in this department of natural science, may
readily be imagined; especially, as the species rapidly multiplied,
when they were supposed to throw some rays of light on certain
obscure geological phenomena. Soon after the appearance of Professor
Brongniart's excellent work, the attention of other naturalists was
directed to this neglected part of creation. The most important memoir,
on account of the number of species, well figured and described in
it, is one by Dr. E. W. Dalmann, published in the Transactions of the
Swedish Academy, for 1826. There is also in the Acts of the Royal
Society, at Upsal, an excellent paper on this subject by Professor
Wahlenberg. Our highly esteemed friend, Dr. James E. Dekay, has also
given in the first volume of the Annals of the Lyceum of Natural
History of New York, some very interesting and ingenious observations
on the nature and the structure of the Trilobites, with a description
of a new genus. These are the principal authorities which have been
consulted in arranging the present work.
[Footnote 4: I cannot let this opportunity pass, without acknowledging
my obligations to Professor Brongniart, for his civilities, when on a
late visit to Paris. Every one whose curiosity leads him to examine the
royal manufactory of porcelain, at Sevres, of which he is the director,
will no doubt acknowledge that his talents as a philosopher, are
rivalled by his accomplishments as a gentleman.]
Our object in the present undertaking being merely to give a monograph
of the species of Trilobites found in the rocks of North America; we
leave to other and abler hands the more difficult and interesting task
of determining with precision the connexion which may exist between
these organic reliques, and the relative ages of the strata in which
they are found.
It is supposed, indeed, that a sufficient number of well characterized
species have not yet been collected and accurately described, to throw
any certain and clear light on otherwise doubtful geological phenomena.
What has been remarked by De Candolle, with regard to botanical
geography, is perhaps true of these fossils as to solving the difficult
problems of geology--"Let us not forget," says he, "that this science
can only be commenced when the study of _species_ has been sufficiently
advanced to furnish us with numerous and well authenticated facts."
We are well aware of the difficulty of settling the line which ought
to divide species. Individuals perfectly identical in all their
parts, are rarely, if ever seen; though a general resemblance may be
easily traced. Among fossils, just discriminations of this kind are
more delicate, than in recent specimens. The hand of time, accidental
causes, and the influence of atmospheric changes often produce such
characters as to render the determination of fossil species an
exceedingly difficult task. We have no doubt, therefore, that a few of
our Trilobites, which are now considered as perfectly identical with
some found in Europe, will upon fuller examination, be discovered to be
dissimilar, and of course certain geological speculations grounded on
the first opinion, be ultimately abandoned.
The geographical distribution of organic remains, is an exceedingly
curious inquiry. If accurately pursued, without reference to any
preconceived theory, it will no doubt furnish much information as to
the comparative ages of the different strata which compose the external
crust of our planet--for that these strata were deposited or formed at
periods of time more or less remote from each other, every one knows,
to be a generally admitted _geological fact_. The occurrence of similar
fossils in districts of country remotely situated from each other,
certainly presents a phenomenon highly interesting to the speculative
naturalist, and apparently indicates that the same powerful and general
causes must have concurred to produce these isomorphous depositions. No
fossils have contributed more to this kind of information, than those
of shells, and as the mineralized species could not be satisfactorily
studied, except by accurately comparing them with those which now
inhabit our seas and continents; the search for shells, has become,
from a simple amusement, the study of scientific men--or, as a writer
remarks, "it was only after the period when it was perceived that
geology and ancient zoology were destined to be enlightened by their
fossil remains, that this research passed from the hands of amateurs
into those of naturalists."[5]
[Footnote 5: We have not unfrequently noticed, both in the writings
and conversation of some geologists, a disposition to sneer at the
subsidiary branches of natural history. Mineralogy and conchology, are
light and mean in their estimation, when compared with the study of
extensive strata and ponderous boulders. Like Irving's testy governor
of Manahatta, who settled the accounts of his clients by placing their
books in the opposite scales of a balance, they decide on the value
of a science, by the absolute weight of the objects embraced by it.
Geology, as well as any other branch of natural history, may degenerate
into a mere love for the curious, or have for its principal aim, the
perfection or improvement of some ideal system of classification,
without advancing a single step further.]
Another curious _geological fact_ appears to be established more
especially by fossil trilobites; it is that precisely the same species
of animal relic, is the most generally diffused over the globe, in
proportion to the antiquity of the rock which contains it. Thus the
transition limestone of England, France, Germany and Sweden, contains
the species called the Calymene of Blumenbach, in common with the same
formation which extends over so large a portion of the United States.
Different genera and species of the trilobite are now found in almost
every part of the globe, and are frequently exceedingly abundant in the
rocks which contain them. That they must have swarmed in particular
places, is abundantly evident from a number of localities in our own
country,--millions, for example, must have lived and died not far
from Trenton falls, in the State of New York. There are very few of
the numerous visiters to that romantic cascade, whose curiosity is
not awaked, by the multitude of these petrified beings, seemingly of
another world, which are there entombed.
Although many parts of the trilobite are now found distributed through
the rocks which contain them, in such a manner as to lead to the
conclusion, that they were separated by decomposition, after the death
of the animal; yet the perfect preservation of others, and the rolled
and disjointed attitudes which we should expect such creatures to
assume when disturbed, lead to the conjecture, that they have been
often suddenly destroyed, and as suddenly enveloped in that earthy
matter, which afterwards became an indurated rock; thus preventing the
separation of the harder parts, by the slow process of decomposition.[6]
[Footnote 6: Vide De la Beche's Geological Manual.]
The fossil remains of the trilobite family, are supposed by most
naturalists to belong to a race of beings now extinct; but from the
strong analogy which exists between them and certain species of
crustaceous animals now living, it is highly probable that they will
yet be found alive. This opinion will not be regarded as visionary,
when it is recollected how large a portion of the surface of the earth
is still unexplored by its enlightened and civilized inhabitants--how
small the number of animated beings are yet known to the scientific
world--and above all the fact, that many animals as confidently
declared to be peculiar to a former world, are now found to be among
the creatures at present in existence. This opinion, we think, is
quite as plausible, and far more interesting, than the blank and
unsatisfactory hypothesis that all the trilobites are confined to an
order of things before the present glorious creation.[7]
[Footnote 7: The incorrectness of the inference that all the genera
and species of fossil animals found in the transition rocks must be
now extinct, will appear from the following extract from Bakewell's
Geology:--"The _Madrepora stylina_, so common in transition lime-stone
rock, is entirely wanting in the secondary and tertiary strata, but a
living animal of this species has been recently discovered in the South
Seas. The Pentacrinus makes its first distinct appearance in the lias;
but is not frequently met with in the upper strata, and disappears
entirely in the uppermost formations: hence it was long supposed
that the species was extinct. A living Pentacrinus has recently been
discovered in the West Indies, and its stem and branches in a perfect
state have been sent to this country." (England.) In the Museum at
Albany, N. Y., I have examined a recent Pentacrinus, which I conclude,
came from the West Indies, from the proprietor's account of the manner
in which he obtained it. It has been a very perfect specimen but the
branches are gradually dropping off.]
There appears to have been known to naturalists, when the improved
edition of Prof. Brongniart's work on the trilobites appeared in 1822,
but 17 well marked species, and out of which he constructed the five
following genera, which he thus characterizes.
_Genus First._ Calymene.
_Body_ capable of contraction into nearly a semicylindrical sphere.
_Buckler_ with many tubercles or folds. Two reticulated eye-shaped
tubercles.
_Abdomen and Post-abdomen_ with entire edges. Abdomen divided by 12 or
14 articulations.
No elongated tail.
_Genus Second._ Asaphus.
_Body_ broad and rather flat. Middle lobe prominent and very distinct.
_Flanks or lateral lobes_ each double the size of the middle lobe.
_Submembranaceous expansions_ extending beyond the lateral lobes.
_Buckler_ semicircular, with two reticulated eye-shaped tubercles.
_Abdomen_ divided into 8 or 12 articulations.
_Genus Third._ Ogygia.
_Body_ much depressed into an oblong ellipsis not contractile into a
sphere.
_Buckler_ edged, a slight longitudinal furrow arising from its anterior
extremity. Posterior angles elongated into points.
_Without any tubercles_ except the eyes, which are neither prominent
nor reticulated.
_Longitudinal lobes_ slightly prominent.
_Abdomen_ with 8 articulations.
_Genus Fourth._ Paradoxides.
_Body_ depressed not contractile.
_Flanks_ much broader than the middle lobe.
_Buckler_ nearly semicircular three transverse furrows on the middle
lobe.
_Eye-shaped tubercles_ none.
_Abdomen_ with 12 articulations.
_Arches_ of the lateral lobes, more or less prolonged beyond the
membrane which sustains them.
_Genus Fifth._ Agnostus.
_Body_ ellipsoidal--semicylindrical.
_Buckler and flanks_ edged--the edges being slightly elevated.
_Middle lobe_ with two transverse divisions, each composed of a single
piece.
_Two glandular_ tubercles on the anterior part of the body.
In 1824, Dr. J. E. Dekay added a sixth genus to the family of the
trilobites, which he describes in the following manner.
_Genus Sixth._ Isotelus.
_Body_ oval oblong, often contracted, not unfrequently extended.
_Head_ or _buckler_ large and rounded, equalling the tail in size, with
but two oculiform tubercles.
_Abdomen_ with 8 articulations.
Frontal process beneath, with two semilunar terminations.
_Post-abdomen_ or _tail_ broad, expanded with indistinct divisions, as
large as the buckler.
_Longitudinal_ lobes very distinct.
This genus, he remarks, will be sufficiently distinguished from the
five genera proposed by _M. Alexandre Brongniart_ in his valuable and
truly philosophical work on the trilobites by the following particulars.
From _Calymene_. By the presence of but two tubercles on the buckler
not reticulated; by the abdomen with but 8 articulations.
From _Asaphus_. By the middle lobe, which is double the size of the
lateral ones; by the absence of a membranaceous expansion on the sides;
by the non-reticulation of the eyes, &c.
From _Ogygia_. By the rolled form, the rounded posterior angles of the
buckler, and the distinct articulation of the longitudinal lobes.
From _Paradoxide_ and _Agnoste_ by characters too obvious to be
enumerated. (See Annals of N. York Lyceum, Sec. Vol. I. pp. 174-5.)
In 1826, J. W. Dalman published in the Transactions of the Swedish
Academy, and also in a separate work, an account of the trilobites
found in the North of Europe, in which he has enriched the family by
a number of fine species, and with the following genera, which he
modestly proposes merely as subdivisions.
_Genus Seventh._ Nileus.
_Body_ short, capable of contraction into a sphere, smooth, convex.
_Abdomen_ with about 8 articulations, without any dorsal longitudinal
furrows.
_Buckler_ sub-lunate, with large lateral eyes.
_Tail_ expanded, not so large as the buckler, without lobes.
_Genus Eighth._ Illænus.
_Body_ ovate oblong, contractile.
_Head_ rounded in front, eyes small, in the temples, very remote.
_Abdomen_ with from 9 to 10 articulations, trilobate.
_Tail_ expanded as large as the head.[8]
[Footnote 8: Some of the species described by Professor Dalman as
included in this genus, we think ought to be referred to that of the
Isotelus.]
_Genus Ninth._ Ampyx.
_Body_ very short, contractile.
_Buckler_ large, triangular, gibbous; eyes not remarkable.
_Abdomen_ short, articulations few (6?), trilobate.
_Tail_ expanded, not so large as the head.
Professor Dalman has two other genera, which he calls Olenus and
Battus, the first is the Paradoxides, and the second the Agnostus of
Brongniart.
In the 8th Volume of Annales des Sciences Naturelles there is a highly
valuable paper "Sur les Trilobites et leurs gisemens," by the Count
Rasoumowsky, in which he describes some new trilobites from Russia;
the one which he has figured and described as a Calymene[9] from
Tzarsko-Selo, undoubtedly belongs to a new genus, very near to the
Isotelus. The middle lobe is visible or naked through its whole extent,
and the lateral lobes near the tail are covered with a thick cuticular
membrane. This genus we propose to call Hemicrupturus, and may be thus
characterized.
[Footnote 9: The editors of the Annales remark that this is not a
Calymene, but that it appears to belong to the genus Asaphus.]
_Genus Tenth._ Hemicrupturus.[10]--_Green._
[Footnote 10: From three Greek words which signify _half-concealed
tail_.]
_Body_ contractile.
_Buckler_ oculiferous and not lobate.
_Abdomen_ trilobate, with 8 articulations.
_Tail_, costal arches covered, middle lobe naked.
The Asaphus expansus of Dalman, and several other known species may be
arranged under this genus.
As Count Rasoumowsky has given no specific appellation to the
fossil above alluded to, we propose to call it after his own name,
_Hemicrupturus Rasoumowskii_. We examined the fine specimen from which
our cast is taken in the cabinet of the Baltimore College, and for this
favour we are indebted to the kindness of Dr. J. J. Cohen, one of the
Professors in that rising institution.
The following list includes _all_ the genera and species of the
Trilobite Family, hitherto described as far as known to the author. It
is taken from De La Beche's Manual of Geology.