Chapter II: Part 2

I am indebted to the Albany Institute for the originals of the models Nos. 11 & 12. They were found at Seneca, Ontario County, New York, in dark, slaty limestone, which also contains cubical crystals of iron pyrites. A fortunate blow of the hammer has fractured the rock which contains this trilobite, so neatly, as to present us at the same time with the petrified animal in an almost perfect state, and also with the mould or matrix in which it was imbedded. This arrangement is beautifully illustrated by our models.

Genus Asaphus. _Brongniart._

This genus derives its name from the Greek word Ασαφης--obscure. It embraces perhaps more species than any other genus of the family of trilobites. About twenty have already been discovered. Most of them are very characteristic and can easily be determined, but as the genus Asaphus, is intermediate between Calymene and Ogygia, it is sometimes a little difficult to decide the genus to which the inosculating species on each side, belongs.

In general, the Asaphs may be known by the body being very much depressed, and by the membranaceous development, which extends beyond the lateral lobes. The middle lobe of the abdomen, is rarely more than one-fifth the width of the body. As the abdomen and tail of the Asaph are the only portions of the animal commonly found entire, the distinctive characters of the genus above given, may generally be ascertained.

Professor Brongniart remarks, that the ribs of the _Asaph_, which correspond in number and position to the articulations of the middle lobe, "are sometimes simple or undivided, at least in the post abdomen, but that they are always bifurcated in the _Calymene_" As far as our observations have extended, these remarks do not apply either in the one case or the other.

The head or buckler of the _Asaph_, is not so deeply divided into three lobes as the _Calymene_; they are, however, quite distinct. The oculiferous tubercles are in some species exceedingly well marked by a reticulated structure.

This genus often occurs at the same localities with the Calymene, though in some instances it seems to occupy rocks peculiar to itself. Dr. John Bigsby, in his list of organic remains occurring in the Canadas, states, that he never found a single species of the genus Calymene, on the north side of the River St. Lawrence, although the Asaphs were very abundant.[23] In his Sketch of the Geology of the Island of Montreal, he however observes: "Of Trilobites, the Asaph genus is the most abundant, they approach nearest the species _caudatus_, of Brongniart. I have found no entire Calymene, but many bucklers or heads of the Blumenbach species, some of them an inch and a half in diameter. They are found whole in considerable numbers in the vicinity of Quebec."[24]

[Footnote 23: Silliman's Journal, vol. viii. p. 83.]

[Footnote 24: Annals New York Lyceum, vol. i. p. 214.]

Asaphus Laticostatus.[25] _Green._ Cast No. 13.

[Footnote 25: From the Latin for "broad ribbed."]

Cauda prælonga, pars ad marginem vix membranacea; cute coriacea,
tuberculis minimis; costis latis, convexis et valde distinctis.

The fragments of this species, which we have examined, comprise ten articulations of the middle lobe, and the corresponding ribs of the sides, all in a very good state of preservation; the extent to which the membranaceous expansion reached beyond the tail and the lateral lobes is very apparent, but it has been unfortunately broken off all round. Our specimen appears to be a natural cast of the internal part of the shell, or the coriaceous covering of the animal.

The portion of this specimen of trilobite which still remains perfect, is two inches long, and three inches and a quarter broad. The middle lobe exhibits the appearance of a very exact and gradually tapering cone, its articulations being rounded and slightly flattened on the top. The ribs of the lateral lobes are nearly straight, slightly arched, broad, rounded, and gradually increase in width from the point of their insertion; they are simple or not bifurcated throughout, and are covered with very minute granulations, which are probably produced by the sandstone in which the animal is mineralized. The membranaceous expansion near the caudal termination, is a good deal prolonged.

The A. Laticostatus occurs in a light coloured ferruginous sandstone, which contains a multitude of other fossil remains, particularly a large species of Productus and of Terebratula. It is said to have been found in Ulster county, in the State of New York, by the late Charles Wilson Peale, Esq., the distinguished founder of the Philadelphia Museum. During the memorable search after the bones of the _Mastodon Giganteum_, in the marl pits of that county, this enterprising naturalist procured our Asaph with many other remarkable petrifactions. The rocks which contain them were probably found not _in situ_, but were masses rolled from the neighbouring Shawangunk mountains,[26] which by some geologists are supposed to be a link in the grand chain of the Alleghanies. Mr. R. Peale, of New York, lately visited the rich repository of fossils in Ulster County, and procured a number of specimens of the A. Laticostatus, all of which he has kindly permitted me to examine. These are much smaller than our cast, but in many instances the caudal elongation is perfectly developed. The A. Laticostatus also occurs in the Helderberg mountains, specimens of which are in the Albany Institute.

[Footnote 26: The Lenape tribe of Indians, who formerly inhabited this district of country, gave the name of Shawangunk to this stupendous ridge of hills a name which has been very properly preserved.]

Asaphus Selenurus.[27] _Eaton._ Casts Nos. 14 & 15.

[Footnote 27: Derived from _Selene_, moon, and _ouros_, tail.]

Cauda semilunari; costis angustis, valde distinctis; abdominis
articulis duodecim; corpore convexo.

I am indebted to Professor Eaton, for two specimens of this very interesting species. In his Geological Text Book, he thus describes it: "Tail crescent-form, or concavo-convex, with the convex side forward, upon which the post abdomen terminates: abdomen contains about 12 articulations, with an abrupt termination equal in breadth to one-fourth of the length of the transverse lunate tail; the articulations of the side lobes gradually incline towards the axis of the body, until the last pair terminate at the tail. Found in transition limestone at Glenn's Falls, and Becroft's mountain, near Hudson. I have a specimen from Becroft's mountain, with part of the original covering of the animal remaining."

When we first noticed the remarkable lunate appearance of the tail of this Asaph, we supposed that it was occasioned by some accident, but there seems no doubt that this conformation is natural. In our specimens of this species, which are not however perfect, the articulations of the abdomen do not exceed 8 in number. The representation of this animal remain given by Mr. Eaton, plate 1, figure 1, is exceedingly inaccurate; it will confuse rather than illustrate the subject. Our cast and the drawing, we believe, are taken from the same specimen, which was kindly loaned by Mr. Eaton for this work. It is but justice to the amiable, industrious, and indefatigable author of the Geological Text Book to remark, that he regrets as much as any one, the insufficiency of his figures of the trilobites, to give any correct idea of the fossils they are intended to represent.

In the cabinet of the Albany Institute there are a number of specimens of the A. Selenurus. One of our models represents the natural mould made by the animal in the rock; the other is an impression taken from it, in order to exhibit the animal in a more satisfactory manner.

Asaphus Limulurus.[28] _Green._ Cast No. 16.

[Footnote 28: From two Greek words, which signify "Limulus tailed."]

Cauda longa, spina munita sicut in Limulo; costis abdominis in
spinis retrorsum flexis, desinentibus.

It is very much to be regretted that the abdomen and caudal end only of this remarkable Asaph have hitherto been discovered; it is, however, exceedingly gratifying that the fragment still remains in so perfect a state. It forms a part of the magnificent cabinet of organic remains belonging to J. P. Wetherill, Esq., now deposited in the Academy of Natural Sciences, of Philadelphia.

Dr. J. J. Cohen discovered a small specimen of this species at Lockport, New York, which he has presented to the Athenæum, in Baltimore.

Eight articulations of the abdomen, and ten of the tail, are all of this fine species that we have seen. The ribs, or costal arches of the abdomen have a deep furrow on their upper surface, commencing at the middle lobe, and terminating near their free extremities; these extremities appear all detached from each other, and end in reflected points or spines, so as to give the side of the animal a serrate appearance. The costal arches of the tail are grooved through their whole extent, and present no spinous terminations. Beyond the membranaceous expansion of the tail, which is somewhat similar to that of the Asaphus Caudatus, there projects a single spine, like that from the tail of the _Limulus polyphemus_; this spine may be traced under the caudal membrane to its insertion into the middle lobe. A portion of the crustaceous shell is still entire, and it seems to have been covered with very minute granulations. A row of large granulations may easily be traced on each side of the middle lobe. Length of the fragment, one inch and a half. Breadth one inch and a fourth.

The A. Limulurus was found in the dark brown, shaly limestone, at Lockport, in the State of New York; it is associated in the same rock with the terebratula and several other fossils.

The singular spinous projection from the tail of this Asaph, furnishes another analogy, between the trilobite and the limulus; an affinity which was suggested by Dr. Dekay; and which has been argued with great ingenuity both by himself and Professor Wahlenberg.[29]

[Footnote 29: See Nova Acta Regiæ Societatis Upsalensis: 1821. Also, Annals of the Lyceum of Natural History. New York. Vol. i. pages 179-185.]

Asaphus Caudatus.[30] _Brünnich. Brongn._ Cast No, 17.

[Footnote 30: From the Latin word for "tailed,"]

Clypeo antice subrotundato, postice valde emarginato, angulo
externo in mucronem producto; oculis exsertis, conicis, truncatis,
distincte reliculatis; post abdomine in caudam membranaceam, acutam
extenso. (Vide Brongniart.)

The middle lobe of the buckler is marked by three transverse plicæ or folds on its posterior part, and its cheeks or lateral portions are triangular; the posterior exterior angles of which, are acute, and considerably elongated. The cheeks are furnished with conical, truncated, semilunar and externally convex tubercles, which were beyond all doubt the eyes of the animal, being reticulated as in those of the Limulus. The middle lobe of the back is narrow, and has twelve articulations. The lateral lobes are composed of double ribbed costal arches. Beyond the lateral lobes and the caudal termination, there is a smooth, thick membranaceous expansion, which forms an acute projection below the central portion of the tail.

The specimen in the Philadelphia Museum, by which I have identified this species, is marked as coming from Ripley, Ohio. It reposes on a fragment of ash coloured limestone--which contains also a mutilated specimen of what seems to be a calymene, and a few small terebratulæ, &c.

Dr. John Bigsby, in his "List of Organic Remains, occurring in the Canadas," states that the A. caudatus is frequently met with, thrown up by the water on the north shore of Lake Superior--on the bank of Rainy river--at the Lake of the Woods, and at several other places. In some localities they are astonishingly numerous, and so small as to be almost microscopic. They occupy indiscriminately limestone of every colour, but are most numerous in that which is brown or crystallized. They are composed of the kind of limestone in which they happen to be embedded.

We have seen a number of specimens of this species in the Albany Institute, in Mr. Wetherill's cabinet, and in the Baltimore Athenæum; but in all of them, the abdomen and caudal extremity only remain perfect: from their exact resemblance, however, to the same parts of the A. caudatus, figured by Brongniart, (plate 2, fig. 4, D.) we have no hesitation with regard to their identity. The description which we have given of the _buckler_, supposed to belong to our Asaph, is therefore taken from Brongniart, whose specimens were found at Dudley, the celebrated locality of the C. Blumenbachii.[31] The coriaceous membrane, which extends beyond the lateral lobes and forms the caudal termination of our species, is not covered with minute dots, as in the European fossil; and if a new name is to be applied to it on that account, it may be called _A. glabratus_.[32] M. Wahlenberg, has given the figure of a trilobite which he calls _caudatus_, but ours cannot be mistaken for that species, to which Brongniart has very judiciously applied the name of _A. meucronatus_.

[Footnote 31: In the first volume, 2d series, of the Transactions of the Geological Society of London, Mr. Weaver has published some highly interesting observations on the fossils found in Gloucestershire, England. The A. caudatus, he states, is there found in the transition limestone, though very much mutilated. (Vide p. 326.)]

[Footnote 32: In the cabinet of G. W. Featherstonhaugh, Esq., I have examined a fine specimen of the A. caudatus, from Dudley, England, but could not perceive the minute dots on the tail, as mentioned by Brongniart.]

The conical eye-like protuberances on the head of this species, are very remarkable, and so much resemble the reticulated eyes of the limulus, as to leave no doubt that they once contained the organs of vision.

Asaphus Hausmanni. _Brongniart._

Cauda rotundata; cute coriacea tuberculis minimis spinulosis tecta.

In De la Beche's Geological Manual, there is a list, of the trilobites which have been discovered in the grauwacke group of rocks. This list we have given in our introduction. Among the trilobites he states that the Asaphus Hausmanni has been found in the United States; as we have not seen the species, and presuming the author to be correct in his locality, we give the following description from Professor Brongniart.

I know, he observes, only the tail of this Asaph, but it is so different from that of other trilobites, that I do not hesitate to establish a particular species, upon the consideration of this part alone. Its general form is that of a semi-ellipsis; the middle lobe represents a very slender cone. The arched ribs of the lateral lobes are perfectly distinct and simple. I cannot perceive in them the slightest appearance of bifurcation. This sufficiently characterizes the species. But that which further distinguishes it from the others, are the small, elevated points, scattered, and of course rough (serrés), with which the skin or epidermis is covered, resembling, in this respect, the tail of the _Apus canceriformis_.

This fragment of an Asaph is in a homogeneous, compact, blackish limestone, which contains no other kind of petrifaction. I know not where it was found. It is in the cabinet of M. de Drée.

On plate 2 of Professor Brongniart's work, he has given figures to illustrate this species; fig. 3 A. represents the whole fragment, and 3 B. two of the ribs of the lateral lobes, magnified to show the arrangement of the tubercles, which are very peculiar.

From the above description it will be readily perceived, that the A. Hausmanni comes very near to the A. Laticostatus. There are, however, many striking differences, which will be obvious to those who compare our cast with the figures of Brongniart. The shape of the ribs, and the tubercles upon them; the form of the middle lobe and of the interstices between the articulations, are all peculiar to each. The elongation of the tail in our species is alone sufficient to distinguish it. We have always been doubtful whether the minute granulations on our species were not produced by the sandstone in which it is petrified.

Upon what authority the A. Hausmanni has been considered as a species belonging to the United States we cannot determine. In the valuable and extensive cabinet of trilobites belonging to the Albany Institute, there are a number of specimens labelled with this name by Professor A. Eaton. If we mistake not, he mentioned to us that similar fragments of this fossil were sent by him to Brongniart, who, we understand, is the author of the list of trilobites found in the manual of De la Beche. The specimens which have been examined, both in the cabinet of Professor Eaton, and in that of the Albany Institute, are certainly not identical with the figures or descriptions published of the A. Hausmanni. Professor Eaton, in his Geological Text Book, at page 31, thus describes his A. Hausmanni:--"Tail rounded, and forming the middle of a circular arc whose centre is in the fore abdomen, near the head; covering tubercled or spined. Found in coral rag on the south shore of Lake Erie. Also, in its underlaying grit slate on the Helderberg." Some other trilobites mentioned in De la Beche's list as occurring in the United States, we have not been so fortunate as to meet.

Asaphus Pleuroptyx.[33] Cast No. 18.

[Footnote 33: From the Greek word for "grooved ribs."]

Corpore depresso; cute coriacea tuberculis minimis; costis
striatis; cauda acuta, brevi.

This species like most other specimens of this genus, in our cabinets, is decapitated--every other part, however, appears to be in a good state of preservation.

The articulations of the abdomen and tail, which cannot readily be distinguished from each other, are seventeen in number. The middle lobe is flat, and regularly tapers to an obtuse lip; it is marked on each side with longitudinal impressed lines or little grooves. The costal arches on their upper side have a deep and narrow channel, running through their whole course. The costal arches of the abdomen have no membranaceous expansion beyond their terminations; this organization is only visible immediately below the end of the middle lobe, where it quickly finishes in an acute point. A large portion of the crustaceous shell remains, and is covered with distinct granulations; those on the tail are the least obvious.

This species approaches very near the A. caudatus, but the grooves on the middle lobe, the smallness of the costal arches, and the limited extent of the membranaceous expansion round the lower portions of the shell, will sufficiently distinguish it.

Two specimens of this Asaph are in the cabinet of the Albany Institute. The one from which our cast is taken, was found on the Helderberg mountains; it is embedded in a light grey coloured limestone shale. The other specimen, which is much smaller, was discovered near the Genessee River, in the State of New York. The rock in which it occurs is identical in its constitution with the other. It contains other species of trilobites, and a number of shells.

Asaphus Micrurus.[34] Cast No. 19. Fig. 3.

[Footnote 34: From the Greek, for "minute tail."]

Cauda attenuata, acuta; corpore valde convexo; costis striatis;
parte marginali vix membranacea.

This fine, large caudal termination of an Asaph is in the cabinet of the Albany Institute--and it is a subject of great regret, that all that has yet been discovered relating to this highly interesting trilobite, is to be seen in this fragment.

There are eighteen articulations of the tail and abdomen, which cannot be distinguished from each other. The middle lobe is composed of a series of straight, distinct, parallel articulations, very convex about the middle, so as to form a kind of longitudinal ridge down the back. The costal arches of the lateral lobes are very distinct, and are longitudinally striated or grooved on their upper surface, particularly those near the upper part of the animal. The membranaceous expansion is very narrow along the sides of the body, and forms a sort of hem; below the central portion of the tail it makes a short acute projection, which seems to be supported by a short costal elongation of the middle lobe. Length two inches and a half.

The A. Micrurus was found in the black fœtid limestone of Trenton Falls, by M. H. Webster, Esq., and by him placed in the rich collection of trilobites in the Albany Institute. The limestone in which this Asaph is embedded, is almost one entire mass of petrifactions. The general aspect of the A. Micrurus is very similar to that of a calymene--but judging from its structure, it could never contract its shell into a spherical figure. Its minute tail, and narrow membranaceous expansion round the terminal edges of the lateral lobes are quite peculiar, and determine it to be an Asaph.

Asaphus Wetherilli.[35] _Green._ Cast No. 20.

[Footnote 35: I have named this species in compliment to my friend, John P. Wetherill, Esq., whose magnificent cabinet of fossils in the Academy of Natural Sciences of Philadelphia, will ever remain as a monument of his discrimination, enterprise, and liberality.]

Clypeo postice arcuato, sulcato; abdominis articulis duodecim;
cauda vix membranacea; cute coreacea vix punctata.

The contour of this beautiful Asaph is very regularly ovate; unlike most of the remains of this genus, the buckler is still attached to the abdomen, though one of the _cheeks_, and a portion of the _front_ are obscured by the rock in which the animal is imbedded. The cheeks form spherical triangles. The oculiferous tubercles, though a good deal defaced, seem to have been circular and not lunate, as in the A. Caudatus. A raised, curved line passes from and over the eye, between it and the lateral lobe of the abdomen. The central lobe of the back is composed of twelve double joints, and that of the tail of six single articulations; where the epidermis or shell is perfect, all the articulations appear single. The last joint of the tail is longer than in any other of our species. The ribs of the abdomen are rather broad, and have a deep furrow scooped out along their upper surface; their extremities, where they can be discovered, are detached from each other, and terminate in reflected points, like those of the A. Limulurus. The costal arches of the tail are delicately grooved, and terminate in the membrane. The membranaceous expansion round the edge of the tail is very narrow, and appears to form no projection beyond its central part. The whole epidermis is finely marked with granulations. Length one inch and three-fourths--breadth one inch and one-fourth.

This interesting species was found in limestone shale, near Rochester, in Munroe County, N. Y.; and is now in the valuable cabinet of the Albany Institute. An accidental fissure of the rock disclosed not only a fine specimen of both the mould and the cast of this animal, but also another individual of the same species in contact with it. From the peculiar attitude which these fossilized animals maintain towards each other, they appear to have been combatants at the very moment when the catastrophe occurred which produced their mineralization. In the Museum of the Garden of Plants at Paris, there is a large specimen of two fossil fish, which are supposed by many to have been destroyed and covered with mineral matter, when one of them was in the very act of swallowing the other. Mr. Bake well, however, who accurately examined this specimen, is of opinion, that the two heads of the fish had been pressed together by the superincumbent weight.

Genus Paradoxides. _Brongniart._

The animals arranged under this generic name, include the organic remains described by Linné as Entomolithus paradoxus, and Brongniart has given the specific appellation which the great Swedish naturalist applied to these singular animals, out of compliment to him, though he considers it quite inappropriate. The late Professor Dalman calls this genus Olenus, and quotes Paradoxides as a synonyme, but the term of Brongniart seems to have the priority, and therefore must be preferred.

The animals belonging to the Paradoxides have the body very much depressed, and the lateral much wider than the middle lobe.

The buckler is nearly semicircular, the cheeks are destitute of eyes, and the front is marked with three transverse furrows. This last character is probably not a permanent one.

But the most distinguishing character, is the prolongation of the costal arches, particularly those of the tail, beyond the membrane which they are supposed to support; the termination of these arches is in teeth or spines. Some species of the Asaph have prolongated extremities to the ribs of the abdomen, but we have never seen them on the arches of the tail.

This genus is said to comprise a great number of species, but the only one found in North America, as far as our knowledge extends, is that described by J. J. Bigsby, in the fourth volume of the Journal of the Academy of Natural Sciences of Philadelphia. As we have not seen the specimen, we add the description of it in the author's own words.

Paradoxides Boltoni. _Bigsby._ Figure 5.

Oval, blind; surface with small tubercles and striæ; clypeus rounded before; exterior angle extending in a broad spine; abdomen fourteen jointed; segments recurved, falcate; tail membranaceous and serrate.

The shape of this individual is oval, approaching ovate; it is moderately flat; the whole length is five inches and four-fifths; its breadth across the middle is four inches and nine-tenths; wherever the cutis is not removed, it is covered profusely and irregularly with small tubercles. The denuded portions in this specimen, for the space of three quarters of an inch from the external margin, is, in a very small degree, depressed, and displays a number of broken and continuous striæ, parallel to that margin. There are no traces of organs of vision. The buckler is nearly the segment of a circle; anterior edge, in the present case, imperfect; it is four inches and three-fifths broad, and one inch and one-ninth long at the centre; it joins the abdomen by a somewhat sinuous transverse line; cheeks and front of equal breadth; the former are flat, but rise at the sharp ridge by which they unite with the front; they are triangular in shape; their outer angles terminating by an acute tip. The striæ mentioned above are here not quite parallel to the external border; the front is a shallow depression; rounded but tapering anteriorly; it is intersected from above on each side obliquely towards the mesial line, by a ridge bifurcating downwards; another smaller ridge nearly bisects the front perpendicularly.

The abdomen and post abdomen are not distinct. The abdomen exclusive of the cauda is three inches and a half long; it exhibits fourteen costæ varying indiscriminately from one-fifth to one-fourth of an inch in breadth, except the three inferior ones, which are rather broader; they occupy the whole abdomen without membranous interspaces, and are separated by a black sulcus, not always well defined, and sometimes a line in diameter. Each costa is canaliculated from the upper and under angle to the tip.

The middle lobe is separated from the lateral by a shallow, rude sulcus, which however, does not always destroy the continuity of the costæ, as they cross it; this lobe is slightly convex, one inch and a half broad at the top, and so continues to the sixth costa, after which it gradually contracts, until at the bottom it is one-fifth of an inch broad, subsiding insensibly into a flat membrane-like surface; its longitudinal sulci pass one inch farther downwards, and expanding a little, unite with the costæ on each side the posterior edge of the space included by them, being dentated.

The lateral lobes are quite flat, one inch and a half broad anteriorly, and, by gradual prolongation, become at the fourth costa one inch and four-fifths in breadth; this dimension is maintained to the ninth articulation, when it slowly decreases to one inch at the bottom; the recurvature of the costæ is gentle in the upper eight, but then decreases rapidly. Their extremities, advancing two-fifths and four-fifths of an inch into the embedding rock, are falcate with their raised black edges, and clearly marked points.

This trilobite was found by Lieut. Bolton, at Lockport, in the state of New York, in the black, shaly, horizontal limestone forming the lower part of the ravine by which the Erie canal ascends the _parallel ridge_ of Lake Ontario. Dr. Bigsby remarks on this locality, "I am not prepared to assign to this limestone its exact place in the series of geological formations; it is above the saliferous sandstone, and therefore more recent than the rocks best known as abounding in trilobites." We have, therefore, in this instance, another fact, which demonstrates that blind trilobites are not confined to a geological period more remote than That which has produced the animals with oculiferous tubercles.

Genus Ogygia. _Brongniart._

In the vast quarries of slate at Angers, in France, there is frequently noticed two very remarkable organic remains, which have for a long time excited the attention of naturalists. To receive these curious relics, Professor Brongniart established the genus, Ogygia, which he thus characterizes. Body much depressed--elongated into an ellipse, terminated in points--nearly equal at its extremities, and not capable of contracting itself into a spherical form. The buckler is bordered by a slight longitudinal furrow, rising from its anterior extremity, and its posterior angles terminating in elongated points. The abdomen has eight articulations, and its longitudinal lobes are not very prominent. The eyes are neither prominent nor reticulated and there are no other protuberances on the buckler.

In Professor Brongniart's original work on the Trilobites, he has described the two specimens from Angers, under the specific names of Guettardi, and Desmarestii, in compliment to M. M. Guettard and Desmarest; and in De La Beche's Manual of Geology, we are informed that he has since identified two other species; one of which is supposed to be found in North America; this he calls _Ogygia Sillimani_; the banks of the Mohawk River, near Schenectady, is the locality from which it is said to have been derived.

As we have not been able to find any detailed account of this species, we have admitted both it and the genus to which it is said to belong into our Monograph exclusively on the high authority of Professor Brongniart, as quoted in the Manual of Geology. We are not ignorant of the species of Trilobites found near Schenectady, and if permitted to offer a suggestion on this subject, it would be, that the description of the American ogygia, was made out by its distinguished author from the fragment of an Isotelus. The Isotelus is not uncommon in that vicinity, and one of its extremities might, even by a very close observer, be mistaken for that of an Ogygia--especially by those who are not perfectly familiar with the Isotelus.

Genus Isotelus. _Dekay._

This fine genus of trilobites was established November, 1824, by my friend James E. Dekay, M. D. It embraces a considerable number of species so analogous to each other, that except in a very few cases, it is exceedingly difficult to point out their distinctive characters. Some of the species of Isotelus, appear to have reached a greater size than any other trilobite. In the cabinet of P. A. Browne, Esq., there is the fragment of one, which must have been fourteen or fifteen inches long.

The Isotelus is found in several parts of North America, but most abundantly in the black transition limestone, in the northern section of the country. The richest locality, not only of this genus, but also of the Calymene and the Asaph, is Trenton Falls, on West Canada Creek, about 13 miles to the north of Utica, in the state of New York. The following extracts from the notes of Professor Renwick, which accompany Dr. Dekay's account of the Isotelus, will give some idea of this vast depository of the medals of ancient zoology. West Canada Creek, is one of the principal branches of the Mohawk River. At Trenton Falls it has worn itself a passage through the rock for the distance of nearly two miles, forming a series of water falls; and has thus laid open to view the strata to the depth of probably 300 feet. The layers of the rock thus disclosed are nearly horizontal, and of various thicknesses: they are composed of limestone, with the exception of numerous thin veins of argillaceous matter. The higher strata are composed of carbonate of lime nearly pure, of a light grey colour and crystalline structure. At greater depths it is more compact and darker in colour, and finally it appears quite black and highly fœtid.[36]

[Footnote 36: See Annals of N. Y. Lyceum, vol. i. page 185.]

Animal remains are contained in every part of the rock; besides several genera of trilobites, we have several species of orthocera. Encrinites and Fungites--Nautili--Terebratulæ and Producti, are quite common. The favosites here are sometimes six inches in diameter, and in such numerous columns, as to have induced the late worthy proprietor of this interesting spot, Mr. J. Sherman, to consider them as analogous in structure to the basaltic columns of Staffa and the Giant's Causeway; he therefore maintains the extravagant theory that these columns are nothing more than gigantic favosites.[37] We visited this famous locality of trilobites not long since, and were almost as much delighted with the sublimity and grandeur of the cataract, and the picturesque and romantic character of the glen, as with the reliques of olden times, which are scattered here in such profusion.

[Footnote 37: See a Description of Trenton Falls, by John Sherman, p. 17.]

The genus Isotelus, derived from Ἱσος, equal, and τελος, extremity, is thus characterized by Dr. Dekay.

_Body_ oval often contracted, not unfrequently extended.

_Head_ or buckler large and rounded, equalling the tail in size, but with two oculiform tubercles.

_Abdomen_ with eight 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.

Other distinguishing marks by which this genus may be known, have been given in our introduction.

Isotelus Gigas. _Dekay_. Casts Nos. 21 and 22.

_Head_ representing a spherical triangle, surface punctate, convex, descending from between the eyes to the anterior border, which has a narrow raised rim; posterior extremity concave and corresponding to the articulation of the abdomen. Eyes elevated, prominent, sub-pedunculated; cornea oblong, lunated, highly polished; _abdomen_ with eight distinct articulations, the middle lobe double the size of the lateral one: these latter are continuous with the middle lobe, have a deep furrow impressed on their upper surfaces, which becomes gradually effaced towards their narrow free extremities. These lateral lobes are rounded at their extremities, and flattened in such a manner as to allow each lobe to slide easily under the lobe immediately preceding. _Tail_ subtriangular, convex, equalling the head in size, with the posterior termination rounded. On the centre of its surface, when accidentally decorticated, a slight elevation may be traced, if the specimen be held in a certain light, which appears to be a continuation of the middle lobe; this extends to within a short distance of the posterior angle of the tail, when it is either entirely effaced or terminates in an abrupt truncation. Another elevation runs parallel to and at a short distance from the edge of the tail. These elevations are connected by obscure parallel lines, imitating the spaces between the lateral lobes. When the tail is fractured on the borders, a semilunar depression is visible, exhibiting concentric striæ. The whole Surface of the animal has a jet black polish. Length from 6 to 12 inches.

The original of our cast is in the cabinet of J. P. Wetherill, and was found near Cincinnati, Ohio. It is of a yellowish colour, and occurs in argillaceous slate. Specimens are common in most cabinets of American fossils. The Lyceum in New York, possesses a fragment of an individual of this species, which must have been at least 17 inches long. Our cast, No. 22, is from the gigantic tail in the cabinet of P. A. Brown, Esq. Mr. Stokes describes the I. gigas as a new species under the name of Asaphus Platycephalus, in Geolog. Trans. vol. i. N. Series. His specimen was found in the limestone of. St. Joseph's, Canada.

Isotelus Planus.[38] _Dekay._ Cast No. 23.

[Footnote 38: The general usage of naturalists is to prefix a short Latin caption to the species which they discover--but as some authors do not follow this fashion, we are satisfied to suffer their descriptions to stand without it. We believe, indeed, that the time is not very distant, when every author will be expected to publish his discoveries in his vernacular tongue.]

_Head_ more rounded than the preceding, and less elevated. _Tail_ flat, rounded. Total length two inches and one-tenth. Breadth one inch and one-tenth. Length of the head, six-tenths--of the abdomen, eight-tenths, and of the tail seven-tenths.

Dr. Dekay is of opinion that this species may possibly prove to be the young of the preceding. The relative proportions of its buckler and tail vary considerably from those of the I. gigas; and the depth of the lateral lobes, which exceeds three-tenths of an inch, would almost of itself determine it to be a new species. The original, from which our cast was taken, is in the cabinet of J. P. Wetherill. It was found near Newport, Kentucky, and occurs in argillaceous slate. The fossil is of a dirty yellow colour.

Isotelus Cyclops.[39] _Green._ Cast No. 24. Fig. 7.

[Footnote 39: From the Greek for "round eyes,"]

Clypeo antice attenuato, plano; oculis rotundis, proximis; cauda
ovata, acuminata.

The head of this species is much more elongated than it is in the two preceding species. The anterior portion of the buckler is much prolonged. The eyes are approximate, rounded, and near the posterior edge of the head. The abdomen is furnished with eight distinct articulations; the middle lobe is scarcely broader than the lateral lobes; tail rather broader than the head, and ovate; posterior termination more rounded than the buckler. Length nearly three inches.

The specimen from which our model was taken belongs to the Albany Museum. No label is attached to it, but I was informed by Mr. Meach, one of the proprietors, that it was found in the western part of the State of New York. It is embedded in an ash-coloured limestone. The specimen is a good deal worn--but the peculiar form of the eyes, and the narrowness of the middle abdominal lobe, clearly distinguish it from either of Dr. Dekay's species.

Isotelus Megalops.[40] _Green._ Cast No. 25.

[Footnote 40: From the Greek for "great eyes."]

Clypeo antice subrotundato, postice arcuato; oculis magnis,
rotundis, eminentissimis; cauda suborbiculari, limbo lato;
articulis abdominis octo.

The buckler in its contour resembles very much the head of the I. gigas; it is, however, rather more rounded before, and arcuated behind. The oculiferous tubercles, are very peculiar, being very large, round, and exceedingly prominent. They have a good deal the appearance of solid hemispheres placed on the forehead of the animal. They are exactly on a line with the two abdominal furrows. The abdomen is composed of eight distinct articulations; the middle lobe is rather larger than the lateral lobes. The tail is suborbicular, convex, and rather less than the head. Length nearly five inches. Breadth almost three inches.

This magnificent Isotelus was obtained near Trenton Falls, in New York, by P. A. Browne, Esq., and now forms a part of his fine collection of fossils, in this city. It occurs in black transition limestone. It differs essentially from the I. gigas of Dekay, in the magnitude, collocation, and contour of the eyes. Those of the I. gigas are oblong and lunate, and nearly half the distance between the anterior and the posterior edges of the buckler; those of the I. Megalops are not only much larger, but they are round, and very near the posterior border of the head.

Isotelus Stegops.[41] Green. Casts Nos. 26 and 27.

[Footnote 41: From two Greek words, which signify "covered eyes."]

Clypeo antice, caudaque postice attenuatis; cute coreacea punctis
minimis.

The head of this species is nearly in the form of a spherical triangle; its anterior edge is vertically flattened all round, but does not produce a narrow raised rim, such as is described by Dr. Dekay, to belong to the I. gigas. The eyes are prominent, and rather nearer the lateral edge of the buckler, than to its posterior border. The shell of the buckler forms a remarkable projection over the top of each oculiferous tubercle, something like an eye-lid. Continuous with the edge of this cuticular projection, there is a curved linear depression, which terminates on both sides, at the edge of the buckler. This kind of suture, though remarkably developed in this species, is not peculiar to it, being more or less distinct in most of the Isoteli. The articulations of the abdomen are lost; there can be little doubt, however, that they were eight in number. The tail is subtriangular, and less in magnitude than the buckler.

This fossil is among the number of fine specimens in the cabinet of J. P. Wetherill. It is in a rolled or contracted attitude, and is somewhat distorted. We have given, however, models of the head and the tail, in two distinct pieces. The external shell, or calcareous covering, is more perfect in this specimen than in any other we have ever seen. A considerable portion of the under side of the anterior part of the buckler, is also well preserved, and perfectly coincides with the figure and description given of it by Dr. Dekay and Mr. Stokes. There is another fragment of an Isotelus in the cabinet of Mr. Wetherill, showing eight articulations of the abdomen, which probably belongs to another individual of this species. The dorsal shell is in a high state of preservation. This species is embedded in clay slate, and was found in Newport, Kentucky.

Genus Cryptolithus. _Green._

Among the numerous organic relics embedded in black limestone at Trenton Falls, in the State of New York, there is often found the fragment of a trilobite which cannot properly be referred to any of the genera already mentioned. Dr. J. Bigsby, in his Sketch of the Geology of the Island of Montreal, has figured and described a fossil which occurs at that place, which approaches in its specific characters to the fragments found at Trenton--but he does not suggest for his relic any name. Professor Brongniart has also represented, plate 4, figs. 5 and 7 A. B. C., the fragments of trilobites from Russia and from Llandillo, in Wales, which seem to differ but little from those above noticed, these are also without names. Under such circumstances, we have thought it expedient to group these relics under the generic term of Cryptolithus, a name analogous to Calymene, Asaphus, Ogygia, and Agnostus, and which may with propriety be applied to the animal, should it ever be discovered entire.[42]

[Footnote 42: Since the above was written, and the C. Tessellatus published, I have received a fine specimen of this trilobite from Professor Eaton, in an almost perfect state, so that the entire animal can now be described.]

_Body_, contractile.

_Buckler_, lunate, convex, outer edge surrounded by a semicircular, reticulated, or tessellated border.

_Front_ or middle lobe of the buckler very protuberant.

_Oculiferous protuberances_, none.

_Abdomen_, much compressed, trilobate.

Cryptolithus Tessellatus. _Green._ Cast No. 28, and Fig. 4.

Clypeo rotundato, fronte valde convexo, capite antice semicirculari
margine tessellato ornato.

Outline of the buckler hemispherical, the edge surrounded by a semicircular border of tessellated or rounded punctures, in three concentric rows in front--on each side near the posterior angle of the buckler, these rows of punctures are more numerous; the front is highly convex; is rounded before, and gradually tapers towards the abdomen. The cheeks form spherical triangles, and are entirely destitute of oculiferous tubercles or any other markings; their posterior angles project beyond the sides of the abdomen. Abdomen and tail very much compressed, and composed of about ten articulations; costal arches of the lateral lobes grooved; tail attenuated. Whole length half an inch.

The Cryptolithus Tessellatus, resembles a good deal the Entomostracites Granulatus of Wahlenberg, and which Dr. D aim an calls Asaphus Granulatus. The figure of this animal given by Brongniart, table 3, fig. 7, appears to be quite imperfect, and is very unlike, except in the buckler, the representation of Wahlenberg's fossil, given by Dalman, table 2, fig. 6. Though the angles of the buckler in the Asaphus Granulatus are much more elongated than those of the C. Tessellatus, it may perhaps be another species of the same genus.[43]

[Footnote 43: The following, is Dr. Dalman's description of the Asaphus Granulatus:--

A. trunco sexarticulato pygidioque lævibus, capite antice
semicirculari margine granuloso, angulis posticis extensis corpore
longioribus.

Animalculum singulare, inversum si inspicitur, lyram forma fere
similans. Caput antice semicirculare, margine distincto, serie
submoniliformi e granulis approximatis ornato, discus capitis
lævis, sed ambitus intra marginem punctis elevatis obsitus. Hic
ambitus, una cum margine, truncum quoque amplecti videtur, ad
pygidii basin usque, ubi in cornua lævia, trunco multo longiora,
abit. Glabella antice fere clavæformis, ad basin utrinque emittens
lobi rudimentum. Truncus brevis lævis segmentis constans tantummodo
sex, rhachide angusta. Pygidium breve, rotundatum, læve; adeo
parvum ut ne quidem capitis disco respondeat.

Obs.--Oculos atque suturam facialem ex autopsia describere licet.

Vide Om. Palæaderna eller de sa kallade Trilobiterna af. J. W. Dalman, pages 50-4. ]

The animal described and figured by Dr. J. Bigsby, to which we have already referred, seems rather different from our species. His specimens were found at Montmorenci, near Quebec, (Canada) more than an inch and a half in diameter. The following are his remarks on this trilobite.[44] "The front of the buckler is remarkably convex, and has on each side near the base, three very small transverse lines, scarcely to be called depressions, corresponding to the sulci so strongly marked in the genus Calymene. There is frequently, but not universally, a very minute pisiform process on the centre of the front. The whole upper edge of the buckler is always surrounded by a very ornamental semicircular border, sometimes semi-elliptical, of punctures placed in the meshes of a net-work in high relief and arranged close together, in rays, passing perpendicularly from the buckler and forming at the same time when observed transversely, curved lines parallel to its upper rim or edge, excepting at the sides, where they diverge, leaving a space occupied by other lines of dottings, parallel to the former, but speedily terminating on the cheeks of the buckler. The lines which are complete from side so side, are four in number. The imperfect additional ones, vary from two to four; the smallest and inner, consisting only of two or three punctures. A plain edging includes the semicircle of punctures. In the beds of these casts, the places of the punctures are shown by small conical elevations, and those of the ridges of the net-work, by corresponding depressions."

[Footnote 44: See Geology of the Island of Montreal, in Lyceum of Nat. History, N. Y. p. 214.]

Should this prove to be a distinct species, we propose to call it _Cryptolithus Bigsbii_.

The _Nuttainia Concentrica_ of Professor Eaton seems also very nearly allied to this species; he describes it as having "four or five concentric arcs of punctures in front of the buckler, separated by alternating arcs of fine elevated ridges." The genus Nuttainia, to which he refers this species, cannot include it, and the N. Sparsa; for these two relics have scarcely a single essential character in common; we have, therefore, confined the genus Nuttainia, to the species which he calls _Sparsa_.

The Cryptolithus Tessellatus is very common at Trenton falls. In the transition limestone at Glenn's falls, in the state of New York, during a very short visit to this place, Dr. R. Harlan procured a large number of this fossil, but only the buckler, the projecting front of which exhibited a pisiform protuberance above the level of the strata. Mr. Eaton says that the N. Concentrica "occurs in the wacke variety of transition of argillite, on the Champlain canal," between the town of Waterford and the Mohawk river. The specimen in my cabinet, from which our cast was made, is from that place.

The Cryptolithus Tessellatus occurs also in the limestone which, according to Dr. Bigsby, overlays the sandstone in the island of Montreal. At most of its localities, it is associated with the Isotelus, the Calymene, and with several species of Asaphus. The Cryptolithus, which is entirely destitute of eyes, being thus found with the oculiferous species, is an interesting fact, and controverts the opinion of Professor Wahlenberg, that the trilobites, which are without eyes belong to a geological epoch more ancient than those which are furnished with oculiform tubercles. That organic remains furnish us with the most satisfactory evidence of the identity or dissimilarity of certain formations, is a disputed point with some geologists[45] It cannot reasonably be doubted, that new and isolated facts have been made the basis of a too hasty generalization. On this subject Count Rasoumowsky makes the following remarks:--"Les divers gisemens des Trilobites ne me semblent pas non plus pouvoir être déterminés avec quelque précision. M. Brongniart parait admettre que les trilobites aveugles ne se trouvent que dans de tres anciennes formations dans des schistes et des calcaires de transitions; mais nous avons donné la description d'un trilobite [without eyes] des bords de la Yaousa prés de Moscow, qui n'appartient certainement pas aux formations de transition, ce qui me donné lieu de croire que de nouvelles recherches et de nouvelles observations, prouveront qu'il n'est pas strictement vrai qu'en France, en Angleterre, en Russie, _il n'existe point de trilobites entiérement privés d'yeux_, comme le dit le savant auteur que je viens de citer." See Annales des Sciences Naturelles, Vol. 8. page 195.

[Footnote 45: See Eclectic Review, for July, 1832.]

Genus Dipleura. _Green._

_Body_, contractile, not much depressed, and slightly tapering.

_Buckler_, pustulous, trilobate, cheeks protuberant, with oblique, annular, oculiferous tubercles.

_Abdomen_, with fourteen articulations, not lobate, the ribs double.

_Tail_, suborbicular, not so large as the buckler, covered with an epidermis.

This genus derives its name from two Greek words, which signify double ribs; many of the trilobites are thus characterized; but in no species, is this organization so remarkable as in those which belong to the Genus Dipleura. The expansion of the tail resembles, in some degree, that of the Isotelus, but other obvious characters sufficiently distinguish it from that interesting genus. The fossils arranged under this section are larger than most other trilobites.

Dipleura Dekayi. _Green._ Casts No. 30, 31, and Figs. 8 & 9.

Clypeo lunato punctato; abdomine quatuordecim articulis duplicibus vix lobatis; cauda suborbiculari; limbo lato convexo integerrimo; oculis oblique deflexis.

The buckler is subtriangular, and covered with granulations; the anterior portion of our specimen being mutilated, we cannot determine its form exactly. The cheeks are very prominent, and swell up gradually towards the oculiferous protuberances, which are oblique, and marked at their apex with a depression, so as to give them an annular appearance. The abdomen is crossed by fourteen double distinct articulations, not interrupted in their course, by the two longitudinal furrows, so common in most of the trilobites; but owing to certain curves or irregularities in the ribs near their lateral termination, a trilobate appearance may in some specimens be detected. Tail suborbicular, convex, and covered with a thick epidermis.

The specific name of this species was given in compliment to Dr. James E. Dekay, of New York, whose valuable paper on the genus Isotelus, first directed my attention to the American trilobites.

The D. Dekayi has been found in several districts of the United States; at Lockport in the State of New York, it is not uncommon. The small specimen from which our cast of the abdomen and caudal end was taken, is in the fine cabinet of Mr. William Hyde, who permitted me to use it with his wonted liberality and kindness. It is said to have been found in Northumberland, Pennsylvania, and occurs in grey carbonate of lime. In the Philadelphia Museum, there is a fine fragment of this species, in which there is embedded some crystals of iron pyrites; it was obtained in Ulster County, New York. In the cabinet of the Academy of Natural Sciences, there is a longitudinal and hollow fragment, filled with ochre, and the oxide of iron; it is labelled from Lockport, New York. At Mount Hope Institution, near Baltimore, there is also a good specimen from the same locality. In the _Clinton collection_, owned by the Albany Institute, there is a large extended fragment, nearly five inches long. It is embedded in brown limestone, and was found in Madison County, N. Y. There are twelve articulations of the abdomen remaining, and the epidermal covering of the tail is distinctly marked with numerous dots. In the same collection there is another large fragment of this species, consisting of the tail and fourteen articulations. It was found in Steuben County, New York; and occurs in grey limestone. It is slightly contracted and very much depressed laterally. There is also a head in the same kind of limestone, from Cazenovia, Madison County, New York. In the cabinet of the Institute there is another specimen of this species, about six inches in length, and nearly perfect; it is also embedded in a similar rock, and was brought from Rochester, Munroe County, New York.

The original of the head from which our cast was made, is in the cabinet of P. A. Browne, Esq., and was found by that enterprising geologist near Lehighton, Pa.

Genus Trimerus.[46] _Green._

[Footnote 46: From the Greek for "three divisions."]

_Body_, contractile, tapering, compressed.

_Buckler_, pustulous, indistinctly lobate, with only two small elevated oculiferous tubercles.