The structure of the tail is similar to that of both A. tardus (Barrande) and A. glabratus (Angelin) but in these species the median lobe of the head is smooth and consists of one plate only, without furrows.

It may be that the tail above figured belongs to a different species, but even if that should be the case it is specially distinct from A. tardus and À. glabratus, for these are both smooth, while ours is striated like A. exsculptus (Angelin), and besides the proportions of the parts are sufficiently different to be of specific value, especially when the character of the surface is taken into account. A. tardus and A. glabratus, both belong to the upper part of the lower Silurian. A. exsculptus to Angelin's Region B, which is the upper division of the Primordial Zone in Sweden.

In Limestone, No. 1.

AGNOSTUS ORION. N. S.

Fig. 2.

Description.-Length and breadth about equal, sub-circular, convex a very narrow margin all round, glabella not quite two thirds the whole length, very convex, a transverse furrow at one third the length from the apex, a small triangular tubercle at each side next the posterior edge; no tubercle visible on the top of the glabella. A fissure from the apex of the glabella to the anterior margin. Length two lines.

This species only differs from A. pisiformis as figured by Salter in the 3rd Edition of Siluria by having the glabella proportion" ally shorter.

Limestone, No. 1. In No. 2 there are two specimens of an Agnostus which resemble this species but more are required to decide whether they are identical or not.

AGNOSTUS CANADENSIS. N. s.

Fig. 3.-a. b.

Description.-Head, obtusely oblong, semi-oval; width, a little greater than the length; a concave border nearly as wide as the glabella all round. Glabella in width, less than half the width of the head, and in length, a little more than two-thirds the length of the head; a triangular tubercle on each side at the neck, and a transverse furrow a little in advance of the mid

length; the tubercle is obscure and appears to indicated by the small indentation forward in the middle of the transverse furrow.

The specimen represented by Fig. 3, a, is provided with a tubercle, but I cannot see in which direction the apex is directed, and consequently am unable to say whether it is a head or a tail. It has the broad margin of Fig. 3, 6, and I think therefore it belongs to the same species. The segment next the thoracic extremity is a little less than one-third the whole length, and about one-third the whole width. The anterior segment is large and convex, extending quite to the concave border, where it is full one-half wider than it is at the suture between it and the smaller segment. The tubercle is situated in the transverse suture, and makes a small indentation in the edge of the larger segment.

Length of the specimens, about two lines.
Limestone, No. 1.

CONOCEPHALITES ZENKERI. N. s.

Fig. 4.

Fig. 4. Conocephalites Zenkeri.

Description.-Length apparently about two inches. Head very convex, nearly semi-circular with a strongly elevated thin sharp margin all round the front and sides, and just within this a wide deep uniformly concave furrow, the width of which is equal to about one third the length of the glabella. The posterior margin is strengthened by the neck segment which extends the whole width of the head, and becomes much elevated on approaching the outer angles. Glabella conical, very convex, most elevated at about the mid-length, with a well defined neck furrow, the posterior lateral furrows directed obliquely forwards at an angle of 45° with the longitudinal axis of the body, their inner extremities separated from each other by full one third the width of the glabella; the posterior lobes sub-triangular, their anterior angles situated at nearly one third the length of the glabella forward excluding the neck furrow and segment; the middle lateral furrows represented by a small depression or indentation on each

CAN. NAT.

side situated on a line drawn across the head passing through the posterior half of the eyes; in front of these a much smaller indentation on each side representing the anterior furrows. The eyes are small and conical, situated on a line crossing the glabella at one half the whole length of the head, their distance from the glabella equal to one-third the width of the neck segment; ocular ridge extending from the eye forward to a point situated a little in advance of the anterior lateral indentation or furrow of the glabella. From the eye a strong ridge runs outwards to the margin of the head in two of the specimens, but in another it is not seen. Between the eye and the posterior margin and situated near the posterior lobe, on each side is a large sub-semicircular tubercle. This elevation is very slight in the small specimens. The surface of the glabella and cheeks adjacent thereto are apparently smooth but the whole of the concave border around the head is ornamented with fine rugose striæ distinctly visible to the naked eye.

Length of head in largest specimen seen eight lines; length of glabella six lines; width of head fifteen lines; width of glabella four lines; distance between the eyes six lines.

Thorax and pygidium unknown. I have not ascertained whether the posterior angles of the head are rounded or produced into spines.

Limestone No. 1.

Genus DIKELOCEPHALUS.

Owen.

In the species which I have referred to this genus, the general form and aspect of the glabella and pygidium and the course of the facial suture are the same as in D. Minnesotensis the type of the genus specimens of which I have before me from the sandstone of the Western States. From numerous fragments of D. Oweni exhibiting the underside of the head, I have ascertained that the facial suture does not separate the eheeks from each other by cuting the fold of the margin. The head is therefore composed of three pieces only, the glabella, hypostoma and united cheeks. This separates the genus from Proetus, some species of which, such as P. striatus (Barrande) have an expanded front margin and a spinose pygidium very like those of D. magnificus. The head of Proetus consists of five pieces. The hypostoma found associated with our specimens is much like that of Proetus, and it is also not unlike that of Ogygia. According to the figure given in

SILURIA, plate 3, fig. 2, representing the sub-marginal fold of the cephalic shield, and the hypostoma attached thereto of Ogygia Buchii, the structure of the head of Ogygia must be the same as that of Dikelocephalus. The affinities of the two genera are still further indicated by the form of the glabella.

Fig. 5.-Glabella and pygidium of D. magnificus.

Description. Eight or nine inches in length. Head large with a short broad obstusely conical depressed convex glabella in front of which there is a broad flat margin with from five to eight obscure radiating ridges. The neck furrow is represented by an obscure shallow groove which is visible in the middle two

thirds of the width but dies out before reaching the sides of the glabella. In front of this there are from one to three shallow pits or faint depressions on each side of the median line representing the glabella furrows. A line drawn across the head at one third the length from the posterior margin would pass through the centres of the eyes nearly. The eyes are annular about one sixth the whole length of the head, situated their own length from the posterior margin and with their centres about the same distance from the side of the glabella. The facial suture runs from the inner anterior corner of the eye forwards and outwards at an angle of about 45° to the longitudinal axis of the body until it crosses a line drawn through the eye parallel with the axis of the body and having gained a point situated outside of this line at a distance from it equal to the length of the eye or thereabout it curves inward and reaches the front margin at a point somewhere near the line. It then appears to run round the margin. Behind the eye its course is, after a short inward and backward curve, directly outwards nearly parallel with the posterior furrow apparently one half the width of the cheek when it curves back and cuts the posterior margin before reaching the angle. On each side of the glabella nearly opposite but a little behind the position of the eye there is an obscure rounded elongated prominence.

Judging from several detached cheeks the posterior front of the head must be very wide and the angles produced into moderately long triangular spines.

The pygidium is somewhat fan shaped, the posterior margin terminating in six triangular points or spines, the outer ones of which are the longest and the inner ones diminishing in length so as to produce a semicircular emargination for the posterior outline. The greatest width of the pygidium is at about one third its total length from the front measuring to the extremity of the longest spine. In front of a line drawn across at this place the contour is nearly semicircular but behind the line the sides are straight or only gently convex and somewhat parallel slightly converging towards each other. The main body of the axis is about one fourth the total length, convex conical and with four shallow concave transverse grooves. Four ribs in each of the side lobes besides a rudimentary ridge along the middle being a continuation of the axis. The surface is marked by fine fissurelike undulating lines.