1S8 G. F. MATTHEW : ILLUSTEATIONS OF 



The head-shield is broadly semicircular, with the élévations and depressions of the 

 surface strongly marked. 



The middle piece is broad posteriorly, and has a strongly sinuate suture ; the dorsal 

 furrow is deeply impressed. The anterior margin is sharply uptiirned, and divided from 

 the forelimb of the cheek by a deep furrow. The glabella is conical, rounded at the sides, 

 and somewhat pointed in front, and the length and width are equal ; on its sides are three 

 pairs of furrows, the two posterior arching backward, the third, short, and more trans- 

 verse. The occipital ring is short, strongly elevated, and bears a small tubercle on the 

 middle, pointed upward ; it is divided from the glabella by a narrow and sharply-drawn 

 furrow. The fixed cheeks are high, prominently arched all the way to the anterior mar- 

 ginal fold, and meet in front of the glabella ; the front limb at that point being nearly as 

 wide as the anterior marginal fold. The eyelobe is short and prominent, and the ocular 

 fillet distinct, especially on the inner surface of the test. 



The movable cheek is one and a third limes longer than wide, and the length of the 

 ocular curve nearly half the width of the cheek ; the cheek is round and tumid in the 

 inner part, M'hich is divided from the folded margin by a strongly impressed furrow ; the 

 marginal fold runs backward in a short, sharply out-turned point. 



The thorax is short, narrows rapidly behind, and consists of fourteen segments. It 

 has a strongly elevated rachis, rapidly tapering in the first five rings, but more gently 

 afterward ; there is a deep and strong furrow along the centre of the ring. The pleurae are 

 narrow and strongly bent down at the ends, the genicïilation being a little more than half 

 way from the rachis ; the furrow is shallow at the rachis but deejjens rapidly to the geni- 

 culation, and extends quite to the extremity of the pleura, whose point is bluntly rounded ; 

 the length of the pleura to the geniculation is equal to the width of the rachis. 



The pygidium is lenticiilar, and nearly one and a half times wider than long. The 

 rachis is distinctly elevated and boimded by furrows that extend to the extremity of the 

 pygidium ; it has four joints beside the half joint in front ; of these rings, the first is 

 wider and more prominent than the others. The side lobes have three furrows, of which 

 the third is short and obscure ; the rib between the first and second furrow is traversed 

 by a short, faint groove. 



Sculpture. — This species does not show any tubercles, except on the mould of the 

 interior, where the apparent ttibercles are only impressions of the larger pittings of the 

 inner surface. The surface of the test of the glabella, occipital ring, and anterior marginal 

 fold has fine granulations ; but on the fixed and movable cheek it has a strongly pitted 

 surface ; and this part of the head-shield is also marked by numerous anastomosing, raised 

 lines, radiating from the dorsal furrow to the anterior marginal furrow, all round the 

 head-shield. 



Length, 24 mm. ; width, 1*7 mm. Head-shield, 8 X 1*7 mm. Pygidium, 2| X ^\ mm. 

 Centre piece of another head-shield, 9 X 18 mm. 



Horizon and Locality. — In the dark grey shales of Div. 1 d St. Martin's. 



■Nabrow Form (Plate II, fig. 5 h) 



The above description applies to the broad form, the one described by Mr. Whiteaves. 

 The narrow form is distinguished by the following characters : — 



