The striæ, originating at the suture, are first directed backward, and thence, gently curving over the nodes, become nearly vertical and thus continue to near the peripheral carina, where they are turned a little backward, and, passing this elevation, they are directed with a slight curve towards the columella.

This fossil possesses all the characteristic features of the Linnæan genus TURBO, to which it was originally referred by M. DE VERNEUIL, who described and named it in honor of the late Prof. B. F. SHUMARD of St. Louis. It differs so essentially from any other fossil of the Upper Helderberg formation, that there are no other forms for comparison. In many of its features it reminds one of the recent Turbo heteroclita, but it is more rotund and the columellar lip is solid and more extended. In its external characters it presents some interesting resemblances to Palæotrochus Kearneyi. The surface striæ are in all respects similar to those of that fossil, and their curvature is made in precisely the same manner. The peripheral carina is almost identical in character, except where it may be invaded by the nodes from above. The range of nodes in the TURBO is represented by the obscure elevations in similar position on the TROCHUS. In the general form of the shell, aperture and columella, there are no points for comparison.

This beautiful fossil, having never been redescribed in America, has been nearly lost sight of, and I believe the name is scarcely or not at all known in our catalogues of fossils. The shell is usually silicified, and is rarely well preserved, though a few good specimens are known. It is nevertheless not rare, as is shown by numerous casts of the interior occurring in some of the western localities. The individuals illustrated are from the cabinet of Dr. JAMES KNAPP, of Louisville, and are the best specimens known to me. An imperfect specimen of large size exists in the collections of New York State Museum.

It is worthy of notice that, among all the American fossils, there has not been found in the older rocks so complete representation of the genera TURBO and TROCHUS as in these examples, both of which occur in the same formation.

Formation and localities. In limestone of the age of the Upper Helderberg group at the Falls of the Ohio, and at other places in Indiana and Kentucky. Some of the larger casts of Gasteropoda, occurring in the same formation in New York and Ohio, are probably of this species.

NOTE ON EUOMPHALUS DECEWI.

On page 56 reference has been made to a specimen of this species, communicated by Dr. ROMINGER, which is illustrated on plate 27, figures 1, 2 and 3. The specimen has been covered on the lower side by an overgrowth of STROMATOPORA, and the mouth is filled by the same parasitic growth which had overlapped the upper and inner side of the volution near the aperture. Besides this enveloping body, the upper and lateral portions of a part of the outer volution have been covered by a Bryozoan which has left its markings, and partially its substance, as shown in the figures. The removal of the STROMATOPORA from the lower side has destroyed the markings of the shell, except upon a small portion of the surface, as seen in figure 2. The shell has been somewhat compressed in a vertical direction; otherwise, it preserves its proper proportions. In consequence of this vertical compression, the baso-lateral angle has been expanded into a kind of projecting carina, as shown in figures 2 and 3.

This shell presents characters not before suspected from an examination of the casts, which is the only condition in which the fossil was for a long time known. Recently the surface markings of the upper side have been illustrated in figures given in the reports of the Geological Survey of Ohio: Palæontology, vol. 1, plates 19 and 20. While possessing the form and general features of EUOMPHALUS, this fossil presents an aperture of peculiar character, being broadly expanded, and somewhat quadrangular on the lower side, and triangular as seen directly in front. The upper margin is sharply sinuate, making a deep retral angle which meets a strong peripheral band, as in PLEUROTOMARIA; but instead of being on the side of the volution, as in that genus, it is upon the summit: in all other respects the characters of the band are the same. This feature is not altogether properly represented in the figure. The appearance

of the fossil is that of a flattened PLEUROTOMARIA,-the upper side of the volutions being depressed towards the spire.

These characters of mouth and peripheral band are scarcely compatible with those of the genus EUоMPHALUS, as understood from descriptions, or as usually represented in the figures of the typical form of the genus. The Euomphalus Wahlenbergii of GOLDFUSS possesses the peripheral band and all the essential characters of our species, and is clearly congeneric with it.

CHENU, in his description of the genus, recognizes a more or less deep sinuosity in the external lip, and the presence of a peripheral band; and Prof. McCor suggests the necessity of subdividing the genus, and separating those "with rounded whorls and a circular, entire mouth," from those with angular volutions and "a slit in the outer lip, as in SCHIZOSTOMA."

If the features described and illustrated in the species under consideration are characteristic of the typical form of the genus ECOMPHALUS, then it seems proper that it should be referred to the family Pleurotomariida; otherwise, this fossil should be designated as a new generic form, for which I would propose the name PLEURONOTUS, with the following diagnosis:

PLEURONOTUS, N. GEN.

SHELL discoid. Volutions slightly oblique to the plane of the shell, gradually enlarging from a minute apex; concave above and below. Umbilical side broad, and the depression shallow; spire concave; external lip with a distinct sinus. Surface, on the summit, and partially on the external side of the volution, marked by a distinct band, to the margins of which the surface-striæ converge on the two sides, and upon which they make a regular retral curve.

The relations of this fossil (E. Decewi) with PLEUROTOMARIA are quite obvious; but unfortunately I have not at this time the means of comparing authentic Carboniferous forms of EvoMPHALUS with the specimen under consideration; and therefore I must leave undecided for the present, its positive relations to that group of fossils.

THE LOUISVILLE LIMESTONES.

NOTE ON THE HYDRAULIC BEDS AND ASSOCIATED LIMESTONES AT THE FALLS OF THE OHIO.

At the Falls of the Ohio and adjacent localities, the lowest beds of the limestone formation are marked by the presence of Halysites catenulatus, and for a long time have been locally known as the " Catenipora beds." This Silurian limestone is succeeded by the great coral-bearing Devonian limestone, which is everywhere, in that part of the country, a well defined geological horizon; and though the higher beds of the formation are distinguished by the presence of other fossils than corals, there is no marked physical change from the base to the upper stratum which is characterized by Spirifera acuminata. The whole is more generally recognized by its numerous corals, and the genera FAVOSITES, MICHELINIA, ZAPHRENTIS, HELIOPHYLLUM and CYSTIPHYLLUM are prevailing forms.* This limestone is succeeded by beds of an argillaceous magnesian limestone, known as the "Hydraulic limestone," which gradually merges above into thin, slaty beds, some of which are highly siliceous, and these are followed by what is known as the "Encrinal limestone;" the whole terminated above by the black slate. This entire limestone formation above the "Catenipora beds" has been generally, if not universally, recognized as of the age and the western extension of the Upper Helderberg group of New York (representing all that was originally included by EATON under the designation of Corniferous limestone and Schoharie grit). I have accepted and advocated this view of the age of these formations, which seemed to be sustained by large numbers of identical fossils from the two distant regions; and I believe that their relative age has not, up to the present time, been called in question.

As might naturally be expected, the subdivisions recognized in the east and in the west do not always coincide, but it is usually quite possible to correlate these different members by a comparison of their fossil contents. The main

*It was from the presence, in this locality, of numerous species of Corals, identical with those of the New York formations, that, in 1841, I recognized these limestones as of the same age.

limestone (the great coral reef, comprising the Onondaga and Corniferous limestones of the New York system) seems to have been originally unbroken, at least from the valley of the Hudson nearly and perhaps quite to the line of the present valley of the Mississippi. It is traceable in unbroken continuance from the Hudson to the Niagara rivers, and through Canada west to Lake Huron, and thence into Michigan; while in a southwesterly direction are the outcrops on the two sides of the Cincinnati axis, extending through Ohio and Indiana, and thence into Kentucky, where it gradually thins out. During the formation of this remarkably extensive coral reef, there could have been no great change in the conditions of the ocean; for not only do these corals indicate an undisturbed and luxuriant growth, but the same genera and the same species prevail over a large part of the above area. It is only in the superjacent beds that we may look for changed conditions, which have given origin to the different terms used to designate the subdivisions of the formation in different parts of the country.

In New York we have the following members of the series, between the Marcellus shale and Oriskany sandstone:

3. Cherty beds, with species of LOXONEMA, The Corniferous

PLEUROTOMARIA, BELLEROPHON, etc.

Upper Helderberg group.

limestone of EATON.*

In the arrangement of Prof. EATON, all the limestone formation between the Schoharie grit and Marcellus shale was termed "Corniferous limestone "-no subdivisions being recognized. In the reports on the Geological Survey of New York, the subdivision into Onondaga and Corniferous limestones was made for the convenience of reference, and on account of the character of the prevailing fossils in the two members. Farther investigation has shown the existence of a peculiar Cherty bed containing characteristic fossils, and also a Calcareous bed with remains of fishes; both of which are distinct from the Onondaga and Corniferous