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SILURIAN TRILOBITES. 



have yet seen is our fig. 7, from the cabinet of Dr. Grindrod, of Malvern. With his 

 usual kindness he has sent me every specimen that could illustrate this or other 

 species. 



A large convex species, 5^ inches long, and nearly 3 inches wide at the shoulders. 

 Foreign specimens occasionally attain the length of 9 inches? The form is oblong, 

 pointed behind, and abruptly truncate in front, the head being nearly a parallelogram, 

 twice and a half as wide as long, and divided by the distinct axal-furrows into three 

 nearly equal parts. The glabella is urceolate, a good deal widest below, where it is 

 wider than the cheeks, and rather abruptly contracted halfway-up ; the front is straight- 

 truncate, and slightly emarginate. The cheeks, separated by broad axal furrows, are 

 decidedly gibbous, the greatest convexity towards the front in advance of the eye, which 

 is placed two thirds up the cheek and not quite halfway-out. 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. 1 do not know the 

 FlG ' 29 ' exterior; but it is figured as granular by Angelin.] 



Neck-furrow strong and broad, but not reaching 

 the angle. No outer marginal furrow to the 

 gibbous cheek. 



The front margin is of most singular struc- 

 ture, and may be described as tricuspid. The 

 narrow edge is so deeply indented, and at the 



a. H. Knighlii, young (Mr. Edgell's cabinet). _ . ' , , , „ 



j, ij. . . ... , , , , same time tolded, that the front portion over- 



b. Front view of the head enlarged. ' r 



hanging the rostral shield (fig. 2 b) forms one 

 projecting angle, flanked by two smaller projections opposite the axal-furrows, exactly 

 like the salient and re-entering angles of a fortification. 



The rostral shield can only be indistinctly seen in fig. 2, at b. It is pointed in front. 

 But the labrum (fig. 10), from a good specimen of Mr. Edgell's, is a flattened quadrate 

 plate, deeply bilobed at the apex, and with parallel sides, no lateral wings, a convex 

 centre separated from the margin by a shallow furrow ; and with a pair of lateral 

 tubercles well developed (as in AsapJtus, to be described hereafter). 



The thorax-rings are convex on the back, but descend so abruptly at the sides as to 

 give a square appearance to the body. The convexity of the back is greater than in 

 H. delphinocephalus. The axal furrows are but very slightly marked ; the fulcrum a 

 very short distance outside them. The facet large, but not flat, a depression followed by 

 a longitudinal ridge occurring near the apex, which is rather abruptly truncate (fig. S a). 



The pleural groove is narrow externally, very deep and strong on the inner surface 

 (see figs. 5 and 8). It separates the ring into two unequal parts, of which the front is 

 less convex than the hinder part, and is smooth, while the latter is squamous near the 



