abruptly bent forward in the centre, but absolutely continuous, though more frequently alternating and interlocking, while often there is no visible departure from a regular curving line.

The ornamentation upon the crests of the stria and the upper half of the interstriate spaces is precisely the same as already described; but the striæ are stronger. The specimen has a much coarser and stronger aspect than any other one observed, and the pyramid is more abruptly expanded from the apex. The single specimen known does not afford satisfactory evidence of specific distinction, and I have therefore recorded it as a variety of the form with which it preserves many characters in common.

Formation and locality. In the coarse arnenaceous shales of the Hamilton group in Schoharie county, N. Y.

The conditions of preservation in nearly all the species of Conularia are such as to preclude any satisfactory determination of the angle subtended by the sides of the pyramid. The specimens have, in nearly every case, been more or less distorted by pressure, and more frequently completely flattened, so that the original form is never fully preserved. In these conditions the measurement of the apical angle is attended with difficulty, and the results are far from satisfactory.

The following species have been carefully measured, and the angle given is the sum of the angles of two adjacent faces-the result corresponding to the angle inclosed between the edges of a flattened specimen. By this mode of measurement C. undulata, in several individuals, gives a range of 21° to 30°, and an average of 25°; C. crebristriata, 20° to 29°, and an average of 241° in two individuals; C. Cayuga gives an angle of 28°; C. continens ranges from 28° to 41°, and in four measurements gives an average of 35°; C. congregata, in four measurements, gives a range of 22° to 29°, and an average of 26°. These variations of the included angle are probably due, in a great degree, to the varying direction of the pressure which has flattened the shell; it rarely happening that this force is exerted in a vertical direction upon the face or upon the angle of the shell, but upon some intermediate point or in an oblique direction.

CEPHALOPODA.

ORTHOCERAS, BREYNIUS.

HISTORICAL SKETCH.

The earliest notice of fossils of this genus, or of generically related forms, from America, so far as known to the writer, was published in England by CHARLES STOKES, Esq.

In 1823 Mr. STOKES published a description of the genus HURONIA, and described the species H. Bigsbyi, H. vertebralis, H. turbinata, H. obliqua, and H. sphæroidalis, from the limestones of Drummond Island in Lake Huron (Notes on the Geography and Geology of Lake Huron, by JOHN J. BIGSBY, M. D.— Trans. Geol. Soc. London, 2d series, vol. 1).

In 1832 Prof. AMOS EATON published descriptions and figures illustrating "Orthocera circularis, O. striata, O. undulata, O. annulata, O. conica, and O. paradoxica." The first four named species were obtained at Thessalon Island in Lake Huron. All these, with the exception of O. conica, appear to have been identified, by EATON, with species described under the same names in SOWERBY'S Mineral Conchology. It is evident from the figure of O. paradoxica, given by that author, that the fossil is a portion of a species of GYROCERAS, from the Upper Helderberg limestone.

In 1834 Prof. H. G. BRONN established the genus ACTINOCERAS, founded upon the illustrations of the Orthoceratites of Thessalon Island, Lake Huron, published in the Transactions of the Geological Society of London. (Lethaa Geognostica.) In 1837, Mr. STOKES described Actinoceras Lyonii, A. Bigsbii, and A. Richardsoni,

from limestones of Lower Silurian age; the genus ORMOCERAS and the species. O. Bayfieldi, O. Backii, and O. Whitei, the last three named species being from Drummond Island; also, Huronia Portlocki, from the same locality (On some species of Orthocerata: Trans. Geol. Soc. London, 2d series, vol. 5).

In 1838 Prof. GERARD TROOST proposed the genus CONOTUBULARIA for certain forms of ORTHOCERAS (which are, in part, referred to ENDOCERAS), and described the following species from the Lower Silurian: Conotubularia Brongniarti, C. Cuvieri, C. Defranci and C. Goldfussi (Mem. Soc. Geol. de France, T. III).

In the same year Mr. T. A. CONRAD described O. constrictum, from the Hamilton group (Rep. Pal. Dept. N. Y. Geol. Survey).

In 1839 Mr. J. DE C. SOWERBY described O. imbricatum and O. virgatum from the Ludlow and Wenlock formation (Murch. Silur. Syst.). These species have been identified with forms in the Niagara group of North America.

In 1840 Dr. D. D. OWEN described and illustrated Orthoceras marginale, OWEN, from the Upper Magnesian limestone; O. undulatum,* O., from the "Magnesian Cliff limestone;" and figured an Orthoceras [= ENDOCERAS], "from the substrata of the Blue and Gray limestones" of Iowa and Wisconsin. He also designated Orthoceras annulatum? and Actinoceras, with double siphuncle, as occurring in the "coralline beds" of the Magnesian Cliff limestone; and cited Orthoceras anellum, CONRAD, from the Blue and Gray limestones (Report on the Geol. Explor. of part of Iowa, Wisconsin and Illinois). [Communicated to the General Land Office in 1840, published in 1844.]

In 1842 Mr. CONRAD published descriptions of the genera CAMEROCERAS and DIPLOCERAS [= ENDOCERAS, Hall, 1847], with the species Cameroceras Trentonensis and Diploceras Vanuxemi (Jour. Acad. Nat. Sci. Phila., vol 8, pt. 2).

Dr. E. EMMONS published Orthoceras multicameratum (CONRAD, in Ms.), from the Birdseye limestone; O. multilineatum, O. Trentonensis [=CYRTOCERAS] and Cameroceras Trentonensis, from the Trenton limestone; Orthoceras æqualis, from the Loraine shales Hudson-river group; and illustrated other forms of ORTHOCERAS from the Trenton limestone, without specific designation (Geol. Surv. of N. Y., Second Dist.).

=

* O. undulatum in this place is apparently a cast of O. annulatum of SOWERBY.

Mr. L. VANUXEM described Orthoceras primigenium, from the Calciferous group; the "Marcellus Orthocera" [=0. Marcellensis], from the Marcellus shale; and O. constrictum, from the Hamilton group (Geol. Surv. of N. Y., Third Dist.).

In 1843 M. F. DE CASTELNAU described and illustrated the following as new species: Orthoceras Hercules, O. conicum, and O. filiformis, from Drummond Island, Lake Huron; Actinoceras Blainvillei, and A. Cordieri, from Manitouline Island, Lake Huron; A. Beaudanti, A. Beaumonti, and A. Dufresnoyi, from Drummond Island; A. Deshayesi, Green Bay; Huronia obliqua, from Drummond Island; and H. Stokesi, from the "Calcaires schisteux de Schoharie." He also described and illustrated Actinoceras Richardsoni (?) STOKES, from Manitouline Island, Lake Huron; and A. Lyoni, STOKES, from Lac des Bois.

He also described two new genera, SIDEMINA and NELIMENIA, which he places under the Cephalopoda, and the species, S. infundibiliformis, from Manitouline Island, and N. incognita, from the Falls of Montmorensi (Essai sur le Système Silurien de l'Amérique).

Mr. CONRAD described Orthoceras anellum, from the Black-river and Trenton limestones (Jour. Acad. Nat. Sci. Phila.).

JAMES HALL described Orthoceras læve [=0. sublæve, d'Orbigny, 1850], from the Onondaga Salt group; O. subulatum, from the Marcellus shale; and O. acicula [=Coleolus acicula], from the Portage group (Geol. Surv. of N. Y., Fourth District).

In 1847 Mr. HALL described Orthoceras laqueatum, from the Calciferous and Trenton limestone; O. moniliforme, O. subarcuatum (=0. Clintoni, HALL, 1877), and O. tenuiseptum, from the Chazy limestone; O. rectiannulatum, from the Chazy and Birdseye; O. recticameratum, from the Birdseye limestone; O. arcuoliratum and O. fusiforme, from the Black river and Trenton limestones; O. coralliferum, from the Utica slate and Hudson-river group; O. bilineatum, from the Chazy, Black-river, Trenton and Hudson-river groups; O. laqueatum var. a, O. latiannulatum, O. strigatum, O. teretiforme, O. textile, O. vertebrale (=O. Olorus, H., 1877), O. bilineatum var. a, O. clathratum, O. undulostriatum, and O. junceum, from the Trenton limestone; and O. lamellosum, from the Hudson-river group; also the following species of ORMOCERAS: Ormoceras (?) gracile, O. tenuifilum and O. tenuifilum var. distans, from the Black-river limestone; and O. crebriseptum, from the

Hudson-river group; also the genus ENDOCERAS, embracing the following species: E. gemelliparum and E. subcentrale, from the Black-river limestone; E. longissimum and E. multitubulatum, from the Black-river and Trenton limestones; E. angusticameratum, E. annulatum, E. approximatum, E. arctiventrum, E. distans, E. duplicatum, E. magniventrum, E. proteiforme var. elongatum, E. proteiforme var. lineolatum, E. prot. var. strangulatum, E. prot. var. tenuistriatum and E. prot. var. tenuitextum, from the Trenton limestone; E proteiforme, from the Trenton and Hudson river groups; also, Gonioceras anceps, from the Black-river limestone (Palæontology of New York, vol. 1).

In 1850 Mr. HALL described Endoceras lativentrum and Ormoceras remotiseptum, from the Trenton limestone; and Colpoceras virgatum [= Endoceras virgatum], from near the junction of the Birdseye and Black-river limestones.

In 1851 Mr. HALL described Huronia annulata, from the Niagara group (Report on Lake Superior Land District: Foster & Whitney.

In 1852 Mr. HALL described Orthoceras abruptum [= Cyrtoceras?] and O. multiseptum, from the Medina sandstone; O. virgulatum, from the Clinton and Niagara groups; and O. cancellatum [=0. subcancellatum, H., 1877]; and identified O. imbricatum, WAHL., O. annulatum? Sow., O. undulatum,* HIS., and O. virgatum? Sow., from the Niagara group; Ormoceras vertebratum and Discosorus conoideus, from the Clinton group (Palæontology of New York, vol. 2).

In 1857 Mr. E. BILLINGS published the following species: Orthoceras cornuum, from the Chazy group; O. Allumettense and O. Minganense, from the Chazy and Black-river groups; O. decrescens, O. hastatum, O. Murrayi and O. Ottawaense, from the Black-river and Trenton groups; O. Huronense, O. Python, O. vulgatum and O. Xiphias, from the Trenton group; 0. Anticostiense, O. balteatum, O. Lyelli, O. magnisulcatum, O. propinquum, O perannulatum, O. Crocus and O. Sedgwicki, from the Hudson-river group; O. formosum, from the Trenton, Hudson-river and Anticosti groups; O. rotulatum, from the Niagara group; O. persiphonatum and O. Canadense (= Huronia vertebralis, STOKES, 1823), from the Middle Silurian; and O. Bucklandi, from the Upper Silurian (Rep. of Progr. Geol. Survey of Canada for 1857).

* The species O annulatum and O. undulatum are identical, the former having precedence in time.