THE FAUNA OP THE ST. JOHN GEOUP. 105 



tiie distance from the same point ; it runs along tlie edge of the lateral margin, iintil it 

 approaches the posterior angle, and there it cnts across the extremity of the marginal fold 

 in a c^^rving line, releasing the genal spine from its connection with the shield. A line 

 drawn from the front (apex) of the glabella, touching the front of the cheek, will intersect 

 the anterior margin, where, on the tinder side of the shield, the suture usually begins ; it 

 varies, however, a little in different individuals. It is a somewhat remarkable fact that, 

 while in the two Bohemian species of the Conocoryphea, C. Sulzeri and Ct. coronatvs, the 

 suture begins quite near the apex, in the Acadian species of all genera of that group it be- 

 gins about one-third of the distance from the front of the shield to the genal angle. 



THOEAX. {Figs. 11-12.) 



This middle region of the body is seldom found in connected segments, but the slates 

 abound with pleurae, having the form and ornamentation of this species. The thorax of 

 the adult is not known, but that of the half-grown animal (14 by 28 mm., var. perhispidusY 

 consists of fourteen segments {Fig. 12). The axis is well rounded, and the rings are about 

 three-fifths of the length of the pleurae ; each ring is grooved more deeply at the sides than 

 on the axial line, and carries a few small obscure spines, ranged along the crests of the 

 bounding ridges. The pleurae are bent downward at the middle of their length, and are 

 strengthened by a wide groove or furrow, which extends well out towards the tip ; the 

 raised edges of the pleurœ are decorated with eight to ten small spines, these being more 

 numerous on the front than on the back edge of each pleura. 



PYGIDIUM. {Figs. 13, 13^1, 13c, 13c;.) 



Among the pygidia of the Conocoryphean type there are two kinds which are of 

 much more frequent occurrence than others ; the smaller of these corresponds in form 

 and size to the pygidium found with the thorax just described. This, therefore, is regarded 

 as the pygidium of Ct. Mattheivi, the other being the tail-piece of Conocoryphe Baileyi. 



This pygidium is reversed semi-circular, being straight or nearly so on the base and 

 arched around at the front of the axis and lateral lobes. The largest is about 4 X 8| mm. 

 The axis is about three-eighths of the whole width, and has a posterior slope extending 

 nearly or quite to the end of the pygidiiim ; it has two rings, beside the articulating facet ; the 

 first one is sharply raised with strong furrows before and behind, but the furrow behind 

 the second ring is only faintly defined : the posterior lobe projects in high relief from the 

 general surface of the caudal shield, and descends abruptly and rapidly to the posterior 

 margin. The lateral lobes are flattened posteriorly ; each lobe has one rib, beside the half 

 rib in front ; the first costal furrow is distinct, the second faint, but neither reach the 

 outer margin ; there is no distinct marginal fold, but the surface of the pygidium is 

 slightly raised towards the outer margin. 



Sculpture. — Each ring of the axis bears four or five minute spines ranged along the 

 crest, and the costal rib has about the same number ; a few similar spines may also be de- 

 tected on the outer part of the half rib, and scattered over the flat surface of the lateral 



' Described on a succeeding page. 



Sec. IV., 1884. 14. 



