equal but sometimes uniform in size, from ten to fifteen in the width of two lines, crossed by excessively fine crowded concentric lines.

This species is allied to S. fluctuosa, but differs in having the areas of the ventral and dorsal valves inclined at an angle which is rather less than a right angle. In its outline it forms nearly an uniform arch instead of being abruptly bent like S. fluctuosa.

The dorsal valve of S. recta (Conrad) is said to have a slight mesial depression, while the ventral valve is flat. S. plano-convexa (Hall) has also a slight mesial depression in the dorsal valve, and is flat or even a little convex in front of the beak of the ventral valve, where this species is concave. It has also a perforated beak, and an area more approximated to the plane of the lateral margins that it is in S. Thalia. The three species are, however, notwithstanding these differences, closely related. Locality and Formation.-Trenton limestone, City of Ottawa. Collector.-E. Billings.

Fig. 7.-Strophomena Hecuba, dorsal valve.

Description.-Subtriangular with usually a linguiform projection in front. Width on hinge-line about two inches; length varying from a little less to a little more than the width.

Dorsal valve very convex, nearly regularly arched from beak to front, only a small space at the hinge extremities compressed, the whole of the remainder of the shell exceedingly ventricose, usually a rounded fold in front which becomes obsolete at one fourth the length, area sublinear, scarcely half a line in width in the largest specimens.

Ventral valve depressed convex near the beak, and concave all round near the margin, area about one line wide and forming an angle of about 1150 with the plane of the lateral margins. Foramen not observed.

Surface marked with fine radiating striæ, ten or twelve in the width of one line, every third, fourth or fifth one of which is twice the size of the intermediate fine ones. The whole surface is besides (in most specimens) ornamented with indistinct concentric wrinkles from one fourth of a line to two lines in width. There are probably fine concentratic striæ, although I have not, (owing to the partially exfoliated state of the specimens examined) been able to detect them.

This species varies considerably in the amount of the convexity of the dorsal valve and in the size of the mesial fold in front Some have a wide flat space in the umbonial region, and in such, on a side-view, the outline of the shell rises from the beak at an angle of about 45o only, while in others, which are more ventricose this angle is full 600 with the plane of the margin.

Sometimes the sides are strongly compressed, so that the shell becomes subcylindrical and greatly produced in front, the length exceeding the width. In some specimens the striæ are nearly all of the same size, but in general they alternate as in the finest marked specimens of S. alternata.

Resembles S. Thalia, but that species has the ventral valve concave nearly to the beak. It is more uniformly gibbous than S. fluctuosa.

Locality and Formation.-Anticosti, Hudson River group.
Collector.-J. Richardson.

DALMANITES BEBRYX. N. s.

Description.-Elongate-oval, tapering from the head to the somewhat pointed tail. Length of the two specimens examined 1 inches each, length of head 5 lines, of thorax about 8 lines, of pygidium 5 lines.

The head is broadly rounded in front and appears to terminate in short spines at the posterior angles, The glabella is broad in front, narrowed behind and covered with small but prominent rounded tubercles about or of a line in diameter and of which there are from 10 to 15 in an area of one line square. The anterior lobe of the glabella is transversely sub-oval and its width about equal to the whole length of the head. It is separated from

the posterior portion of the glabella by strong deep furrows directed obliquely forward and outward. The distance between the inner extremities of these furrows is about 12 lines in a specimen 1 inches in length. The second and third lobes are united into one large obliquely triangular lobe with a small transverse pit at the inner margin representing the second furrow. The fourth or posterior pair of lobes are obscurely preserved in the specimens, but they appear to be small. The neck furrow seems to be strongly marked quite across the base of the glabella and the neck segment rather prominent. The eyes as partly exhibited in one of the specimens are rather small, their diameter being one line or perhaps rather more. They appear to be distant a little more than their own length from the posterior margin of the head.

The segments of the thorax are not well preserved in the specimens, but there appear to be eleven. The axis when crushed flat four lines wide at the fifth segment and three lines at the last.

The pygidium is triangular; the middle lobe convex, elongate conical, and with from fifteen to twenty segments becoming gradually more numerous in a given space as they approach the posterior extremity. The side lobes have each about ten pleura all of which are distinctly grooved along the middle. The pygidium appears to terminate in a rounded point a little turned upwards. I have not seen the margin of the pygidium and have not therefore ascertained its characters.

From the appearance of the specimens I think it almost certain that the posterior angles of the head are produced into short spines.

Several specimens of the pygidium of this rare species and one individual nearly entire but flattened by pressure have been found at Ottawa and are now in the collection of the Survey. I am indebted to Col. Jewett, of Albany, for the loan of the specimen figured. It is more perfect than any of ours.

Locality and formation.-City of Ottawa, Trenton limestone. Occurs also in the State of New York in the same Rock. Collector.-E. Billings.

Description.-Elongate-oval, posterior angles of head produced into short spines, proportional length of head thorax and pygidium apparently 5, 7, 5, total length about one inch and a half.

Head, excluding the spines, very nearly a perfect semi-circle, with a shallow concave marginal groove all round the front and sides, and a strongly defined neck-furrow extending across at less than one line from the posterior margin; glabella equal to the whole length of the head, moderately convex in front, the anterior lobe transversely oval, twice the width of the neck-segment, not defined at the sides in front, but confluent with the surface of the cheeks. The anterior furrows have their inner extremities separated by a space equal to their own length, extending obliquely outwards to points situated a little forward of the inner front angles of the eyes. The middle furrows have their outer extremities opposite the mid-length of the eyes and extend inward in a direction gently inclined forward until their inner extremities are a little within one third the width of the glabella at mid-length from each other. The third furrows are opposite the posterior angles of the eyes, parallel or nearly so with the middle pair and about the same length. The neck furrow is well defined quite

across the glabella. The sides of the glabella are curved a little inward at the posterior lobes and then outwards to the outer extremities of the anterior furrows. The neck segment is large and has its posterior margin rather strongly elevated. The cheeks are moderately tumid. The eyes are semicircular, prominent, one fourth the whole length of the head, about their own length from the posterior and a little more than their length from the anterior margin; the distance between their centres appears to be about one twelfth or one fifteenth greater than the length of the head. The surface of the glabella is ornamented with small rounded tubercles of various sizes, the largest being about one fifth of a line in diameter at the base and, in general, distant once or twice their own width from each other. Surface of cheeks not yet distinctly observed but appears to be smooth. In none of the specimens are the lenses of the eyes preserved.

Thorax with eleven segments; axis well defined and apparently as wide as the side lobes, but this character cannot be sufficiently determined, as all the specimens are crushed. Length of the thorax once and a half the length of the head.

The pygidium in the only specimen that I have seen in which any considerable portion of it remains attached to the body, has the posterior extremity broken away. Judging however from the curves of the posterior margin I think it probable that there is no terminal spine as there is in most of the species of this genus. There are about ten segments in the axis and apparently ten in the side lobes. If the pygidium have no terminal spine the proportional lengths of the specimen figured would be very nearly as follows:

On comparison it will be seen that this species differs from D Bebryx in the form of the glabella and in the number of seg ments in the central lobe of the pygidium.

Locality and Formation.-City of Ottawa, Trenton limestone, very rare. Collector.-E. Billings.