50 SILURIAN TRILOBITES. 



as there really are definite characters on which we can rely, it is thought best to follow 

 the general practice, and describe them separately. 



The cabinets of Dr. Grindrod, of Malvern, Mr. E. Hollier, Mr. Tennant, Mr. Mushen, 

 and the British Museum, have furnished the chief materials. 



Description Pour or five inches long; ovate ; length as to width varying from 10 to 



6, to 8] to 6 ; gently convex ; the thorax longer than either head or tail ; the latter about 

 equal to the head, excluding the produced mucro ; axis of the body much more than half 

 the width of the sides. 



Head semicircular, exclusive, of the slightly produced front or the long stout posterior 

 horns, which are broad at the base and reach the seventh or eighth thoracic ring. Glabella 

 coarsely tubercular, widened above, more than one third the width of head ; the forehead- 

 lobe a transverse rhomb, separated from the upper side-lobes by deep, broad, oblique 

 furrows, which nearly meet ; the lateral lobes and neck-lobe all nearly equal in width, and 

 together equalling the forehead-lobe ; the first and second lobes run straight across, and leave 

 but a narrow ridge down the middle ; strong axal furrows separate the glabella from the 

 triangular cheeks, on the surface of which the large pyramidal eyes occupy a variable ex- 

 tent ; a lunate depression surrounds their outer edge, and this is sometimes extended 

 over more than half the width of the cheek, sometimes barely half, giving a considerable 

 difference in appearance. The length of the eye, which is sharply curved, is uniformly 

 from the first basal furrow to the middle of the upper one ; eyelid with a deep concentric 

 groove ; lentiferous surface considerably broader forwards j lenses about 240, 8 or 10 in 

 a vertical row. In several perfectly preserved specimens the corne.a is present, and it is 

 distinctly convex over each lens, the intermediate surface being ornamented with tubercles 

 and granules, so as to leave no doubt of its being the true exterior ; it is, too, continuous 

 with the other portions of the preserved shell. The cornea does not rise, as in some other 

 species, into elevated ridges between the lenses, but is flat in some specimens, in others 

 it sinks down between them. Occasionally a lens (or two) is undeveloped and very small, 

 among other perfect ones. The facial suture exactly circumscribes the glabella in front, 

 falls perpendicularly to the eye, and arches outwards and upwards from its lower angle to 

 the outer margin of the head, on the lower face of which it extends along the margin further 

 back than on the upper surface (PI. IV, fig. 4). The cheek-pieces are united in one (as 

 in all the genus) across the front, and there is no extra piece (or rostral shield) inserted 

 between them above the labrum. 



The latter is parabolic, obtusely pointed, the sides a little waved, and the base of 

 attachment extended ; a transverse furrow within the lip is connected with a marginal 

 longitudinal one on each side ; a pair of lateral strong indentations indicate a second furrow 

 above. 



Round the head a strong furrow separates a broad margin, but ceases at the base of the 

 spines, and there nearly meets the equally strong neck-furrow, which is arched down at 

 its end. The margin in front of the head is more or less produced into an obtuse point. 



