Part 11

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. Green. Cast No. 25.

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. Green. Casts Nos. 26 and 27.

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.

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.

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. "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."

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.