FIG. 1. Hyolithes communis.

2. H. Americanus.

3. H.

micans. 4. H. princeps. In these diagrams a represents the rate of tapering of the shell on the ventral side; b, the transverse section (except in 3 b, which is the inner surface of an operculum enlarged two diameters). The small figure in 3 a represents the apical portion of a specimen. N.B.-All these species vary slightly in the rate of tapering.

Genus HYOLITHES, Eichwald.

In the following description of new species of Hyolithes, I shall call the side of the fossil which is most flattened, or from which there is a projection in front of the aperture, "the ventral side." Directly opposite is the "dorsum." The lateral walls, whether consisting of two sloping planes, as in fig. 2, or rounded as in the other figures, I shall designate simply "the sides." The "width" of the aperture is the greatest distance between the two most projecting points of the sides. This is sometimes close to the ventral side as in fig. 2. The "depth" is the distance between the median line of the ventral side and the dorsum, and is at right angles to the width. That part of the ventral side which projects beyond the aperture is the "lower lip." The "ventral limb" of the operculum is that side which is in contact with the lower lip, when the operculum is in place, in the aperture. The

F

"dorsal limb" is the opposite side of the operculum, in contact with the dorsum. In some of the opercula there is a point around which the surface markings are arranged concentrically; this is the "nucleus."

The following species occur in the pebbles and boulders of a conglomerate which constitutes an important formation on the south shore of the St. Lawrence below Quebec. The age of the rock in which these pebbles are found, is not yet certainly determined, but it is, at all events, near that of the Potsdam.

H. COMMUNIS. This species attains a length of about eighteen lines, although the majority of the specimens are from ten to fifteen lines in length. The ventral side is flat (or only slightly convex) for about two-thirds the width, and then rounded up to the sides. The latter are uniformly convex. The dorsum, although depressed convex, is never distinctly flattened, as is the ventral side. The lower lip projects forward for a distance equal to about one-fourth or one-third the depth of the shell. In a specimen whose width is three lines the depth is two lines and a.half.

The operculum is nearly circular, gently but irregularly convex, externally and concave within. The ventral limb is seen on the outside as an obscurely triangular, slightly elevated space, the apex of the triangle being situated nearly in the centre of the operculum. The base of the triangle forms the ventral margin. This limb occupies about one-third of the whole superficies of the external surface. The remainder, constituting the dorsal limb, is nearly flat, slightly elevated from the margin towards the centre. On each side of the apex of the ventral limb there is a slight depression, running from the nucleus out to the edge. On the inside there is an obscure ridge, corresponding to each one of the external depressions. It is most prominent where it reaches the edge. These two ridges meet at the centre, and divide the whole of the inner surface of the operculum into two nearly equal portions.

The surface of the operculum is concentrically striated. The shell itself in some of the specimens is covered with fine longitudinal striæ, from five to ten in the width of a line. The shell varies in thickness in different individuals. In some it is thin and composed of a single layer, but in others it is much thickened by concentric lamina, and thus approaches the structure of a Salterella. There are also fine engirdling striæ, and sometimes obscure sub-imbricating rings of growth.

This species has been found at Bic and St. Simon.

Fig. 1, b, representing the transverse section, is not so distinctly flattened on the ventral side as it is in most specimens.

Collected by T. C. Weston.

H. AMERICANUS.-Length from twelve to eighteen lines, tapering at the rate of about four lines to the inch. Section triangular, the three sides flat, slightly convex or slightly concave, the dorsal and lateral edges either quite sharp or acutely rounded. Lower lip rounded, projecting about two lines in fullgrown individuals. Surface finely striated, the striæ curving forwards on the ventral sides, and passing upwards on the sides at nearly a right angle, curve slightly backwards on the dorsum. In a specimen eighteen lines in length, the width of the aperture is about six lines and the depth about four, the proportions being slightly variable.

The operculum has a very well-defined conical ventral limb, the apex of which is situated above the centre, or nearer the dorsal than the ventral side. The dorsal limb forms a flat margin, and is so situated that when the operculum is in place, the plane of this flat border must be nearly at right angles to the longitudinal axis of the shell. In an operculum six lines wide, the height of the lower limb to the apex of the cone, is two and a-half lines, and the width of the flat border, which constitutes the dorsal limb, about one line.

This species occurs at Bic and St. Simon; also at Troy, N.Y., where it has been found abundantly by Mr. S. W. Ford of that city. It is Theca triangularis of Hall, Pal. N.Y., vol. I., p. 213, 1847. As that name was preoccupied by a species previously described by Col. Portlock, Geol. Rep. on Londonderry, p. 375, pl. 28 A, fig. 3a, 3b, 3c, 1843, it must be changed. It is a very abundant species, and varies a good deal.

The Canadian specimens were collected by T. C. Weston.

H. MICANS.-This is a long slender cylindrical species, with a nearly circular section. The rate of tapering is so small, that it amounts to scarcely half a line in length of eighteen lines, where the width of the tube is from one to two lines. The largest specimen collected is two and a-half lines wide at the larger extremity, and if perfect would be four or five inches in length.

The operculum does not show distinctly a division into a dorsal and ventral limb. It is of an ovate form, depth somewhat greater than the width, the nucleus about one-third the depth

from the dorsal margin. Externally it is gently concave in the ventral two-thirds of the surface; a space around the nucleus is convex, and finely striated concentrically. On the inner surface there is a small pit at the dorsal third of the depth, indicating the position of the nucleus. From this point radiate ten elongate ovate scars, arranged in the form of a star, the rays towards the ventral side being the longest. None of these scars quite reach the margin.

The shell and operculum are thin and of a finely lamellar structure, smooth and shining.

Occurs at Bie and St. Simon; also at Troy, N.Y.

Collectors, T. C. Weston and S. W. Ford.

Sometimes numerous small specimens from half a line to three lines in length are found with the operculum on the same slab.

This shell appears to me at present to constitute a new genus, differing from the majority of the species of Hyolithes in its circular section, the operculum not divided into dorsal and ventral lines, and in the remarkable system of muscular impressions on the interior. Barrande has figured an operculum of the same type, differing from this in having only three instead of five pairs of impressions. They are, however, arranged on the same plan in both the Canadian and Bohemian species.* It is possible that our species may be a Salterella.

H. PRINCEPS.-Shell large, sometimes attaining a length of three or four inches, tapering at the rate of about three lines to the inch. In perfectly symmetrical specimens, the transverse section is nearly a semicircle, the ventral side being almost flat, usually with a slight convexity, and the sides and the dorsum uniformly rounded. In many of the individuals, however, one side is more abruptly rounded than the other, in consequence of which the median line of the dorsum is not directly over that of the ventral side, and the specimen seems distorted. This is not the result of pressure, but is the original form of the shell. Sometimes, also, there is a rounded groove along the median line of the dorsum. The latter is somewhat more narrowly rounded than the sides. Lower lip uniformly convex, and projecting about three lines in a large specimen. Surface with fine stria and small sub-imbricating ridges of growth. These curve forwards on the ventral side. In passing upwards on the sides, they

Systême Silurian, &c., vol. III., pl. 9, fig 16 H, and fig. 17.

at first slope backwards from the ventral edge, and then turn upwards and pass over the dorsum at a right angle to the length. When the width of the aperture is seven lines, the depth is about five. The operculum has not been identified.

Collected by T. C. Weston at Bic and St. Simon.

FIG. 5. Interior of the ventral valve of 0. gemma, enlarged about five diameters. aa, the two small scars at the hinge; bb, the two central scars; c, the smal! pit near the hinge; dd, the two principal muscular scars; g, the groove in the area.

6 Interior of the ventral valve of O. desquamata, Hall, enlarged 24 diameters.

7. Interior of the ventral valve of Obolus Apollinis, Eichwald, copied from Davidson's "Introduction to the study of the fossil Brachiopoda."

GENERIC CHARACTERS.-Shell unarticulated, ovate or suborbicular, lenticular, smooth, concentrically or radiately striated, sometimes reticulated by both radiate and concentric striæ. Ventral valve with a solid beak and a small more or less distinctly grooved area. In the interior of the ventral valve there are two elongated sub-linear or petaloid muscular impressions, which extend from near the hinge line forward, sometimes to points in front of the mid-length of the shell. These are either straight or curved, parallel with each other or diverging towards the front. Between these, about the middle of the shell, is a pair of small impressions, and close to the hinge line a third pair, likewise small, and often indistinct. There is also, at least in some species, a small pit near the hinge line, into which the groove of the area seems to terminate. In the dorsal valve there are six impressions

⚫ Engraved from a figure kindly drawn for me by Thos. Davidson, Esq., F.R.S., of Brighton, England. The specimen is from the original locality of the species, Troy, N.Y. Collected by T. C. Weston