Part 8

Asaphus Laticostatus. Green. Cast No. 13.

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, 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.

Asaphus Selenurus. Eaton. Casts Nos. 14 & 15.

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. Green. Cast No. 16.

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.

Asaphus Caudatus. Brünnich. Brongn. Cast No, 17.

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. 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. 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.

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.