ORTHOCERAS PROFUNDUM. PLATE XXXVII, FIGS. 7-9. Orthoceras profundum, HALL. Descriptions of New Species of Fossils, etc, p. 48. 1861. 66 66 66 66 66 66 Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 76, pl. 7, fig. 8. 1862. Illustrations of Devonian Fossils: Cephalopoda. Explanation of plate 37, figs. 3-6. 1876. SHELL straight, regularly and gradually enlarging from the apex to the aperture. Transverse section circular. Apical angle 4°. Initial extremity unknown. Chamber of habitation well developed. Its full extent has not been observed. Air-chambers, septa and siphuncle unknown. The test, as preserved on the chamber of habitation, has a thickness of nearly 5 mm. Surface marked longitudinally by sharp ridges, distant from each other two to four mm. where the tube has a diameter of about thirty-five mm., with very fine intermediate striæ, which are visible only under a strong lens. These longitudinal ridges and the interspaces are crossed by regular, sharp, transverse, crenulating striæ, of which there are seven in the space of five mm. There is a gentle sinus in the transverse ornamentation over the ventral side. The internal mould retains the imprint of the strong longitudinal ridges, and the transverse striæ. This species, in its surface-markings, resembles O. Creon, from the Schoharie grit; 0. Edipus and O. Egea, from the Hamilton group; the four species constituting a natural group with the cones fluted. It differs from O. Creon in its more gradual enlargement and distant longitudinal ridges. And from 0. Edipus it is distinguished by the absence of smaller intermediate ridges and annulations, and by its much coarser concentric striæ. It has not the annulations and low undulations of the tube, as in O. Ægea. Formation and localities. In the Upper Helderberg limestone at Williamsville, and Black Rock, Erie county, N. Y. ORTHOCERATA OF THE HAMILTON GROUP. In the eastern part of the State, where the strata above the Marcellus shales are composed of coarse and finer shales without calcareous matter, the Orthoceratites are very rarely seen. It is only where these shales, in their western extension, become in some degree calcareous, that we find these fossils in any considerable number; and as the group becomes attenuated in the same direction, and the formation consists almost entirely of soft, calcareous shaly beds, the Orthoceratites diminish in number, and become extremely rare, except in a few irregular or concretionary calcareous layers, where some specimens have been found as far west as the shore of Lake Erie. The species in their geographical distribution are essentially limited to the zone mentioned, which has a considerable breadth in its gradation from the coarser materials on the east, to the finer calcareous shaly beds on the west. Owing to this condition, we have by far the larger proportion of specimens coming from localities in the central portion of the State. In the same horizon or zone we have also the greatest development among the Gasteropoda, and few species only of both classes are found in the more westerly extension of the formation, and fewer still in the coarse beds of the extreme eastern portions of the group. This partial limitation of the species to a certain zone is probably not alone due to the physical or mineral composition of the sediments, but in some degree to the depth of water required for their development; for while the deposits on the east are clearly littoral in their character, those of the west are off-shore or deeper sea deposits, and carry a much larger proportion of Brachiopoda than of any other class of fossils. At the same time, the periodical oscillations to which this original shore-line and sea-bed have been subjected, have served to give a wider horizontal distribution than would have occurred in a permanently quiet sea-bottom. It is an interesting fact, however, that while the distribution of the Orthoceratites and some other forms is so clearly affected by the causes mentioned, the Nautilus is known from almost the most easterly outcrops of the formation, to the extreme western limits of the State, being most abundant in the central The smaller Goniatites, which are nowhere numerous in beds above the Marcellus shale, have an extreme westerly extension, and are more abundant in Canada West than in New York. area. The Marcellus shale, however, which is regarded as the lower member of the Hamilton group, must be considered in a somewhat different aspect. The Goniatite limestone of this shale, which is known in the most easterly exposures of this formation, continues to the Genesee valley, and is known as an interrupted calc reous band, as far as Lake Erie This limestone bears numerous forms of Cephalopoda, more especially the Orthoceratites, Goniatites, and some Nautiloid forms throughout its range, from Schoharie county to Cayuga lake; while the thinning extension of the stratum and its associated shales carry one form of Orthoceras (O. subulatum) as far as the Genesee valley. The rocks of this group, as a whole, although very fertile in the number of individuals, are comparatively poor in the variety of forms. Among the twenty-six species described, only six may be said to occur at all abundantly. In the softer shales of the group, the surface-markings are often preserved, but the specimens are usually much distorted from compression. In the Marcellus shales, O. Marcellense in the harder and coarser beds, and O. subulatum in the softer shales, the latter continuing into the central members of the group, are the characteristic and common species. The softer shales of the middle and upper portions of the group have furnished a greater variety and abundance of individuals. The beds of the upper portion contain few forms, and these without any special character; O. Bebryx continuing into the lower Chemung. 35 SECTION a.-Robust forms. ORTHOCERAS ERIENSE. PLATES XL, FIGS. 1-4; LXXXVII, FIGS. 1, 2. Orthoceras robustum, HALL. Illustrations of Devonian Fossils': Cephalopoda. Explanation of pl. 40. 1876. Not 66 66 BARRANDE. Eriense, HALL. Catalogue Am. Pal. Fossils, S. A. MILLER, p. 174. 1877. SHELL very large, straight, robust, regularly enlarging to the aperture. Transverse section circular. Apical angle 8°. Initial extremity unknown. Chamber of habitation well developed, having a length equal to twice its transverse diameter through the centre, with a diameter at the last septum of three-fourths the diameter at the aperture. The tube regularly expands to the aperture, which is slightly contracted. Aperture entire, with a gentle retral curve on the ventral margin; margins acute. Air-chambers regular, numerous, having a depth of from ten to fifteen mm., gradually becoming more numerous toward the apex. The internal cast of the walls is smooth and flat, with a minutely longitudinal, striate band around the anterior margin of each air-chamber, with more irregular, slightly undulating, concentric striæ over the central portion Septa thin, smooth, having a concavity equal to an arc of 1160, or a depth greater than that of the chambers. Sutures straight and horizontal. Siphuncle large, straight, cylindrical, with a diameter of eight mm. where the tube has a diameter of seventy-five mm. The test has a thickness of nearly one mm. on the chamber of habitation. Surface cancellated; marked by regular striæ of growth, interrupted by fine longitudinal striæ. The internal mould is essentially smooth, with the septal sutures but slightly indented. The very fine, longitudinal and transverse striæ over a portion of the chamber walls are characteristic but not prominent. A specimen preserving an apparently entire chamber of habitation, and two of the adjacent air-chambers, has a length of twenty-one centimetres, and a diameter at the aperture of ninety-five mm. A septate fragment containing thirteen air-chambers has a length of 155 mm. This species differs from O. Bebryx in its larger size, more distant septa, and cylindrical siphuncle. It more nearly resembles O. Pelops and O. Zeus of the Schoharie grit, but it has not the constriction of the chamber of habitation of the latter, and the prominent areola around the siphuncle of the former species. Formation and localities. In the Hamilton group on Lake Erie shore, and at Otisco, Onondaga county, N. Y. ORTHOCERAS BEBRYX. PLATES XXXVIII, FIG. 10; XXXIX, FIG. 2; LXXXIII, FIG. 14; LXXXIV, FIGS. 11, 12. Orthoceras Bebryx, HALL. Illustrations of Devonian Fossils: Cephalopoda. Explanation of plate 39, figs. 1, 2. 1876. SHELL robust, straight, regularly enlarging from the apex. Transverse section, allowing for the degree of compression, subcircular. Apical angle eight to ten degrees; the variation being due to the compressed condition of the specimens. Chamber of habitation not fully observed. Air-chambers regular, increasing in depth from the apex, and varying in different individuals from six to ten mm. Septa smooth and thin, so far as observed. Sutures, in specimens not distorted by compression, straight and horizontal. Siphuncle moniliform, expanding between the septa, and having a diameter equal to, or two-thirds, the depth of the air-chambers. The septa are usually macerated, or broken from compression, and the position of the siphuncle has not been satisfactorily determined. One small fragment, referred to this species with doubt, retains the septa, and shows the siphon in a slightly excentric position. The test has not been preserved. The casts of the interior indicate a transversly lamellose-striate surface. A fragment, embracing a portion of the chamber of habitation and seventeen of the adjacent air-chambers, has a length of 220 mm. |