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and the wbole surface covered with strong undulating wrinkles. The two species although allied and occoring in strata which are most probably of nearly tbe same age are nevertheless decidedly distinct.
Judging from the figures given in the Palaeontology of NewYork I think it probable that neither of the species there referred to I. crassicauda are identical with the European form.
The specimen represented on Plaie 4 Chazy may be a fragment of a large individual of this species but those on Pl. 60, Trenton, I think are not. I have never seen a fragment of the true I, crassicauda in the Silurian of Canada.
Associated with the specimen above figured is the head of an individual of this species that must have been a little more than three inches in total lengi h.
I beg to express my obligations 10 the Geological Society of London for ihe loan of a specimen of the true I. crassicauda with wbich to compare this species.
Locality and formation. Mingan Islands, and also Island of Montreal, Chazy. Colleciors. Sir W. E. Logan, J. Richardson.
ILLÆNUS Bayfieldi. (N. s.)
Fig. 6. Fig. 4.—Nlænus Bayfieldi. View of the thorax of a rolled up specimen,
5.-View of the head.
6.–View of the pygidium. Description. Oblong, distinctly trilobed ; length two or three inches; width three fourths the length, central lobe rather more than one third the whole width. Proportional length of head, thorax and pygidium about as 9, 8, 61.
The head is transversely oval in outline, the width twice the CANADIAN NAT.
VOL. IV. No. 6. length, rather evenly convex, most prominent in the centre, the front margin broadly rounded, the posterior margin trilobed by the dorsal furrows which are extended forward to about the middle of the head but are only distinct for one fourth that distance; they at first incline towards each other and then becoming very obscure curve outwards; on each side of the central lobe the posterior margin is nearly straight as far as the eye when it gradually curves forward and outward for one half the length of the head when turning a broad rounded angle it merges into the front margin. In consequence of this peculiar form of the posterior margin the genal angle in this species is in the front half of the lateral margin of the head. The eye is of moderate size lunate and within one fourth of its length from the margin. The facial suture curves forward so as to cut the front margin considerably within a longitudinal line drawn through the eye; behind the eye its course is remarkable as it turns outwards and runs parallel with the margin which it reaches at about three fourths the length of the pleurae. The lower angle of the eye is distant from the dorsal furrow a little less than half the width of the central lobe of the posterior margin. The width of the cheek piece on a line drawn transversely across the head at one third the distance from the eye to the front is nearly equal to half the distance between the eyes. In a vertical view of the head neither the full width of the cheek piece nor the position of the genal angle can be seen as the outline is fore-shortened, consequently in the figure above given the width appears less than it really is.
Thorax of ten articulations, axis of thorax square, the length and breadth being the same, moderately convex, well defined ; the fulcra of the pleuræ are at about one third the width of the axis from the dorsal furrow, the intervening space flat.
Anterior edge of pygidium convex at the axal lobe, obliquely truncated from the fulcrum, the axis either not at all or only very obscurely defined.
Surface smooth with the exception of the front of the head where there are at the margin the usual transverse fissures.
This species was discovered by Admiral Bayfield, R. N., during his survey of the Gulf of the St. Lawrence. A well preserved spe cimen is in the Cabinet of the Geological Society of London among the fossils presented by Admiral Bayfield. During the present year 1859, Sir W. E. Logan visited the Mingan Islands and procured numerous specimens at Trilobite Bay the original locality.
Dedicated to the discoverer Admiral Bayfield.
ILLÆNUS AMERICANUS. (N. s.) Description.—Oblong, distinctly trilobed, length, two or three inches ; width about three-fifths the length; proportional length of head, thorax, and pygidium, as 12, 9, 8.
Head large, transversely oblong or sub-oval, length two-thirds the width, convex most prominent in the centre, behind strongly trilobed by wide and deep dorsal furrows, which, towards their anterior extremities have a sigmoid curve inwards and outwards. Front margin somewhat straight or gently convex ; posterior margin straight as far as eye and then gently curved forwards and outwards to the broadly rounded genal angle which is situated in the front half of the lateral border. The eye is not well preserved in our specimens, but enough remains to show that it is not more than two lines in length in a large individual, and situated rather more than half its length from the margin; it appears to be prominent, and is situated at a distance from the dorsal furrow equal to half the width of the axis. The facial suture reaches the front margin a little within the parallel of the eye ; behind the eye its course cannot be ascertained from our specimens,
Thorax of ten segments; axis a little more than one third the width of the whole animal, moderately convex, when not distorted about one-fourth longer than wide, about one-ninth wider at the first than at the last segment, sides nearly straight.
On each side of the axis there is a flat space between the dorsal furrow and the bend of the pleuræ ; the width of this space is rather more than one-third the width of the axis. The pleuræ are bent at the fulcra at an angle of 450 and at a little more than one-third their length from the side of the axis.
The pygidium is comparatively small, its length being only two-thirds that of the head, it is largely truncated at the ends, the two lateral margins thus formed being straight and in length nearly half the length of the whole pygidium; the width of the pygidium is twice its length. The dorsal furrows are strong at the margin but die out at less than one-third the length, and the axis is therefore not defined all round.
The surface is remarkable. On the head it is thickly covered
with short squamose wrinkles, of which there are from six to eight in one line. On the tail these seem to radiate irregularly from the axis as a centre.
This species is related to I. Bayfieldi, but differs in its proportions, its head being larger and the axis of the thorax not square, but longer than broad; the eye is more distant and the surface not smooth. I. crassicauda bas a much larger pygidium, with a conical axis, well defined all round.
Locality and formation.—Trenton Limestone, City of Ottawa. Specimens with all the parts in place rare, as indeed are all the species except I. Bayfieldi.
ILLÆNUS ConradI. (N. s.)
Fig. 9. Fig. 7.—Illænus Conradi. View of the head of a rolled up specimen.
The width of the cheek pioces cannot be seen in this view
on account of the foreshortning. 8.-Nlænus Conradi. Pygidium of same specimen. 9.-Illænus Conradi. Dorsal view, shewing the 8 segments of
of the thorax.
Description.—Oblong, distinctly trilobed, central lobe less than one-third the width at the neck segment, the whole width threefourths the total length. Proportional length of head, thorax, and pygidium, as 54, 41, 4.
Head transversely sub-fusiform, the lateral extremities outside and in front of the eye terminating in obtusely rounded points ; width measured from point to point a little more than twice the length ; front margin convex along the middle with a gentle broad concave sinus in front of each eye; posterior margin strongly trilobed by the dorsal furrows, straight from the furrow to the bend of the pleuræ, then curving backwards to a point behind the eye and thence forward and outward to the lateral extremity. The dorsal furrows are deep and broadly concave at the margin, but become obsolete at about one third the length of the head; they curve a little inwards and they are distant from each other one-third the whole width of the head. The eye is small, sub-globular, abruptly elevated all round the lower, outer and
upper sides, but on the inner side even with the surface; the distance between its outer side and the dorsal furrow appears to be a little variable, but is always more than half the width of the axis of the thorax at the first segment, or about one-sixth the whole width of the head; it is distant from the posterior margin rather less than its own diameter. The facial suture turns outwards and cuts the posterior margin at a point just behind the outside of the eye; it cuts the front margin on a parallel passing half-way between the eye and the dorsal furrow.
Thorax with eight segments, the axis very convex and well defined by nearly straight sides ; it gradually tapers so that the width of the last segment is only about two-thirds that of the first. The space on each side between the axis and the bend of the pleuræ is perfectly flat. The bend of the first pleura takes place at one-third its length or half-way between the axis and the parallel of the outer side of the eye, in the last pleura it is a little more distant.
The pygidium is snb-quadrilateral, the front margin straight with the exception of the convex elevation of the axis in the middle third ; the lateral extremities are largely truncated, straight, aud at an angle of about 80° with the straight portion of the anterior border; the posterior margin is gently convex. The axis is very prominent in front but becomes obsolete or scarcely at all defined behind. The width of the pygidium is not quite twice the length.
The surface is strongly punctate.
The fragments such as the heads and tails are not uncommon but perfect specimens extremely rare. The following are the measurements as nearly as they can be made out from a single rolled up specimen which has the lateral extremities of the head, broken off, but is in other respects beautifully perfect. Length of head in straight line............ 51 lines.
following curvature........ 7 "
at last segment......
- last pleura.... Length of Pygidium.....