120 G. F. MATTHEW : ILLUSTRATIONS OF 



in the middle half so as to narrow the posterior lobe of the glabella, but is nearly straight 

 in the outer quarters ; the occipital ring appears to have a low tubercle at the middle, on 

 the axial line. The two lobes of the glabella and the neck ring are remarkably short on the 

 line of the axis of the shield ; their width, collectively, is only half of the width of the 

 glabella at the anterior of the two furrows in the examples known. The specimen is 

 defective where the anterior furrows would come, and so it is not known whether they are 

 present or not. The posterior margin had a flat fold, widening toward the suture, and 

 was divided from the fixed cheek by a distinct, but rather narrow and shallow furrow. 

 The fixed cheek is strongly indented by the eyelobe at both extremities, and is nearly 

 half the width of the base of the glabella : the eyelobe is short, has a parabolic curve, 

 and is narrow and not prominent ; the suture behind it exceeds it in length, and is strong- 

 ly bent outward in a sigmoid curve; the chord of the anterior extension of the suture is 

 one and a half times longer that that of the eyelobe, and this part of the suture has a long 

 curve forward across the marginal fold. 



The feature in this trilobite which strikes one as most remarkable, is the enormous 

 width of the marginal fold of the free cheek, which is paralleled only in P. Bennettii, 

 described by Mr. Salter. As in that species also, the inner area of the free cheek is compar- 

 atively small ; its peculiarly graceful outlines were formed by the double sigmoid curve 

 of the suture on one side, and the parabolic curve of the cemented suture of the marginal 

 fold on the other side ; along this line the cheek is elevated. 



The Thorax, of seventeen free segments, with the pygidium, is elliptical-ovate with 

 the extremities of the segments closely overlapping, and scarcely shewing free points, except 

 in the last six or seven segments. The rachis is broad, and tapers regularly, but narrows 

 more rapidly from the eighth segment, and quite rapidly from the fourteenth segment ; 

 the first two segments are broader than the average, but all the rings are comparatively 

 narrow. The first four pleurae (opposite the genal spine) are not much longer than the 

 rings of the axis, and are somewhat obtuse, but the succeeding pleurae gradually extend 

 into long, recurved points, so that at the tenth pleura they are twice as long as the ring ; 

 from the tenth to the fourteenth, the pleurae terminate in these gradually lengthening, 

 falcate points, and are emarginate on the posterior edge at the extremity of the plem-al 

 groove. The last three pleurae are suddenly shorter than the preceding, but the points 

 are progressively more extended toward the tail. 



The Pygidium is broadly quadrate posteriorly, with rounded angles. The axis occupies 

 a comparatively small part of it, is pointed at the extremity and has two lobes, of which the 

 anterior, owing to a depression across the middle, has the appearance of being divided in 

 two. The lateral lobes of the pygidium are each traversed by a curving shallow furrow, 

 originating at the side of the anterior lobe, and fading out about half-way from the end of 

 the pygidium. 



The Hypostome has the doubleur attached ; this is marked by distant strise, similarly 

 to the under side of the marginal fold of the free cheek. The central body is broadly 

 rounded in front and the anterior lobe is large in proportion to the rest of the hypostome, 

 and is spread out at the sides. The posterior part of the hypostome is subquadrate behind, 

 and has rounded angles ; the posterior lobe is short longitudinally. 



Sculpture. — This is an unusually smooth species. The head-shield between the sutures 

 is ornamented with obscure, scattered tubercles. The inner part of the free cheek is 



