A Monograph of British Trilobites

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Palĉontographical Society, 1883 - Paleontology - 224 pages
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TRILOBITE1

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Page 165 - The head is more than a third of the whole length, and longer than the thorax, which in its turn, is longer* than the caudal shield. The head is semi-oval, rather pointed in front, and has very short posterior spines ; it is broadly depressed around the margin. The...
Page 75 - ... is wide, semicircular, or less; the outer cheeks, occupying the greater part of the head, are strongly punctate, margined all round by a continuous furrow, and produced into a long head spine, — the border smooth. The eye very far forward, as in E. Sedgwicki, and the facial suture rising so high as to cut the outer margin much in advance of the middle of the head, separating a very small free cheek. The glabella is not nearly so wide as the cheeks ; it is parallel-sided, apparently not much...
Page 165 - The glabella portion is scarcely marked out : the eyes are placed nearly halfway up the head ; they are small (two lines long), the facial sutures curving out boldly beneath them, and cutting the posterior margin more than half way out from the axis. Above the eye they form a narrow ogive, and nearly follow the front margin. On the underside of the head the vertical furrow on the epistome shows distinctly through the cast. The labrum [hypostome] is imperfect, but exhibits a strong marginal groove,...
Page 166 - The pleunc are flat as far as the fulcrum, truncate at their ends, and have but a slight groove, which reaches two-thirds of the length. The fulcrum is at one-third in front, and less than half way out in the middle pleurse. The caudal axis extends three-fourths down the smooth tail, very indistinctly marked above, but in some specimens crossed by several faint rings, and is always prominent at the tip.
Page 166 - Isotelus and Basilicas ; the course of the facial suture is characteristic in both. It differs from its associate (A. affinis ?) not only by the facial suture, but by the scarcely pronounced axis of the tail. And from As. Powisii, with which it might be confounded by casual observers, the want of any tail-furrows except obscure ones on the axis, and the very slight convexity of the glabella, will easily separate it. It grows to only half the size of that species. Locality. — UPPER TREMADOC slate,...
Page 206 - The whole head is covered with the peculiar squamous lineation characteristic of the family Asaphida ; its peculiarities are more particularly described below.
Page 121 - The axis is rather narrow, and not much distinguished from the sides, the furrows being quite continuous across. There are eight of them, the upper not stronger than the rest ; and all are deep furrows, only rather less broad than the intervening ridges. They arch across the axis, which is only slightly convex, and pass direct across the sides, which are gibbous externally, but rather flattened above. The eight furrows abruptly cease at rather beyond halfway down the tail : on the sides they cease...
Page 120 - It is small, oval, prominent, and subtended by a flattened base. The facial suture runs nearly direct to the front margin from the eye, and beneath it turns abruptly outwards, gaining the outer margin considerably in advance of the facial suture. [On the cast the cheek is both granulate and punctate. I do not know the I0' 29- exterior; but it is figured as granular by Angelin.] Neck-furrow strong and broad, but not reaching the angle.
Page 133 - Our specimen may be altered in shape by the pressure accompanying cleavage ; but in the figure some allowance is made for this. If not sufficiently so, still the form must have been a very wide and rounded one, and can scarcely ever have had the shape of the species next described, although evidently closely allied to it. Locality. — UPPER TREMADOC ROCKS. Northern face of the Garth hill, at the mouth of the Traeth Bach, Merionethshire, in company with abundant specimens of Angelina and other trilobites...
Page 206 - The fulcrum is, of course, far outwards; and is formed by a short forward bend of each pleura, which then continues in the general direction, is sharpened anteriorly for rolling, and curves forward at its blunt end ; the foremost pleurae are rapidly shortened, the whole of the lateral portions of the great head projecting beyond them (fig.

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