F. R. Coicper Reed — On Phacops (Chasmops) Marri. 243 



The neck-segment is only about 0"15 inch broad, and is strongly- 

 rounded and prominent ; it is separated by a strong neck-furrow 

 from the base of the glabella, and this furrow is continued laterally 

 as a deep narrow groove limiting the cheeks posteriorly, but it 

 shallows and terminates before reaching the genal angles. 



The cheeks ai'e triangular, not more convex than the glabella but 

 higher along the posterior portion of their inner border. They 

 terminate at the genal angles in long flat spines, closely pressed 

 against the body, and grooved by a continuation of the marginal 

 furrow. At their fixed end they are of considerable width, but 

 narrow at first rather rapidly to about the level of the second body- 

 ring, beyond which the tapering is very gradual. The left spine is 

 partly preserved and reaches down the whole seven and a half 

 thoracic rings on that side, at which point it is broken ofi". 



The axial furrows are narrow, but deep and straight as far forward 

 as the anterior end of the first lobe. The cheeks rise steeply from 

 them. At the anterior end of this first or "cat's ear" lobe the 

 furrow curves outwards and widens into a broad groove, bounding 

 the cheek anteriorly and overhung by the great frontal lobe of the 

 glabella. 



From the highest portion of the cheek which is adjacent to the 

 axial furrow there is a gentle slope down to the outer margin, where 

 a narrow rounded groove — the marginal furrow — bounds it. Out- 

 side this furrow is a broad, slightly convex, smooth border, 0*2 inch 

 •wide ; this is prolonged backwards into the genal spines, and 

 anteriorly runs round the front of the head-shield, w^here it is 

 reduced to a quarter of its width by the overhanging of the frontal 

 lobe of the glabella. 



The ej'es are large and lunate, extending nearly f the length of 

 the triangular first glabellar lobes. A deep crescentic channel 

 bounds them externally, sweeping round their base. The posterior 

 end of each crescent is about half the length of the eye from the 

 axial furrow, and the anterior end is almost on this furrow. 



The cheeks and glabella are finely granulated and covered with 

 small round tubercles, the largest of which are situated on the 

 triangular lobes and the portion between them. The smooth, non- 

 tubercular character of the border offers a striking contrast. 



The facial suture is seen to curve round the front of the glabella 

 and, apparently, is supra-marginal, but this part of the specimen is 

 not well preserved. From the rounded lateral angles of the great 

 frontal lobe this suture runs backwards and inwards in a nearly 

 straight line to the eye, at the posterior end of which it bends out- 

 wards in a convex-forward curve and appears to lie in a slight 

 groove. It cuts the outer margin at a point almost on a level with 

 the posterior end of the eye. 



The axis of the thorax is very convex and is of nearly uniform 

 width, which is rather more than half that of the pleura3. The axial 

 furrows are deep. The pleura3 are flattened ; the fulcrum is well 

 marked and is situated at about one-third of their length from the 

 axial furrow. Each pleura is horizontal and at right angles to the 



