Part 12

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 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.

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. Green.

Body, contractile, tapering, compressed.

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

Abdomen, with thirteen distinct, double articulations divided into three lobes by a slight longitudinal furrow.

Flanks, or lateral lobes, not so broad as the middle lobe.

Tail, tapering to an obtuse point, pustulous, and marked with ten articulations.

This genus resembles in some respects both the Calymene and Dipleura. The form of the buckler, the position and structure of the oculiferous tubercles, and the scarcely lobate divisions of the abdomen, will readily distinguish it from the Calymenes. The articulations of the tail, not being covered with a shelly crust, is a character too obvious to confound it with the genus Dipleura. There is, we think, a beautiful chain of gradations of resemblances, between the Isotelus, Dipleura, Hemicrypturus and Trimerus. The lobes of the abdomen of the Isotelus are very distinct, and the articulations of the tail are hid by a broad thick shelly crust. The lobes in the Dipleura are scarcely apparent, the ribs more numerous; and the covering of the tail much smaller. The lobes of the Hemicrypturus are like those of the Isotelus; but the lateral ones only of the tail are covered. In the genus Trimerus the lobes are like those of Dipleura, but the articulations of the tail are exposed.

Trimerus Delphinocephalus. Green. Cast No. 32, and Fig. 1.

Clypeo semilunari, antice compresso; oculis minimis, enimentissimis; articulis duplicibus vix lobatis; cauda attenuata; corpore tuberculata.

In the rich cabinet of American fossils in the Albany Institute, there are two fine specimens of this species, and I am indebted to that rising and liberal institution, for the use of them in the present work. Our cast is made from the smaller and more perfect specimen of the two. The outline of the buckler forms an irregular semi-ellipse. The front is convex between the eyes, and very much depressed anteriorly, so as to form a sharp edge. The posterior part of the buckler is marked with a transverse groove parallel with the articulations of the back. The cheeks are small and triangular; the small elevated eye-shaped tubercles being placed in the middle, nearly equidistant from each of the angles. The eyes are not reticulated, the summit of each tubercle only presenting a plain oval foramen. The middle lobe of the abdomen is much broader than the lateral lobes, and has 13 distinct, double articulations. The side lobes are curved, and each costal arch is flattened anteriorly near their lower extremities, no doubt for the purpose of enabling the animal to roll itself into a ball. The tail is tapering, and is composed of ten articulations. The crustaceous covering is here more thickly deposited than on any other part. The entire shell seems to have been covered with minute elevated dots; these are beautifully distinct on the buckler and on the tail. Whole length of the specimen described, not quite two inches.

The other specimen of this species in the cabinet of the Albany Institute, is a large caudal end, three inches and a half long, entirely perfect. Both of these fossils were brought from Williamsville, Niagara county, New York. They occur in a dark shelly limestone, filled with other petrifactions. The calcareous matter which has mineralized the trilobite, in this instance, as in most others, is of a much darker hue than the surrounding rock.

Genus Ceraurus. Green.

Body, very much depressed, and slightly tapering.

Buckler, scarcely trilobate; cheeks large, flat, with small remote oculiform tubercles; posterior angle of the buckler spinous.