SPHiEREXOCHUS. 77 



Larger specimens have lately occurred ; and the finest I know, in Dr. Grindrod's collec- 

 tion, is nearly two inches long. Of this the head occupies more than a third of the whole 

 length, and the glabella is very large, occupying, as seen from above, four fifths of the 

 width, and quite overhanging the narrow front margin. It is, excluding the neck-segment, 

 nearly a true hemisphere, and has a pair of large orbicular lobes at the base, deeply cir- 

 cumscribed, and further apart from each other than their own diameter. The furrow that 

 bounds each of these lobes is broad, sharp, and equal in depth all round, leaving no com- 

 munication with the body of the glabella (figs. 4, 5, G). Above these lobes, on each side, 

 are two faint impressed lines, which represent the upper furrows (see fig. 5, a) ; of these 

 the one next to the round basal lobe is placed at a less distance from it than the 

 diameter of that lobe, at about the point of the head's greatest width, and the upper one 

 at an equal distance in advance of it towards the front. The cheeks are small in com- 

 parison with the glabella, and hang vertically from its sides (fig. 5, cc), like a pair of 

 lappets from a cap or helmet ; they are oblong, and have a thickened margin. The small 

 convex eye is placed very near the glabella, and below the middle of the head ; the facial 

 suture runs outwards from it, and reaches the exterior margin, which it cuts obliquely, a 

 little in front of the posterior angle, as is fig. 6 ; in front of the eye it continues parallel 

 to the glabella, and runs along the edge of the narrow front margin, leaving the free 

 cheeks connected beneath by a narrow band (fig. 5, 6). The free cheek is hatchet-shaped ; 

 and the small eye (fig. 5, c) occupies the inner corner, supported on a fold of the crust, 

 which truncates, or even indents it below. The eye is thus pushed up into a supine 

 position ; it is short, oblong, and very convex. The lenses are numerous, larger in size 

 than the granulations of the general surface, and placed near together, less than half their 

 diameter apart. In this specimen we have not the outer surface sufficiently perfect to 

 enable us to say whether the cornea is raised into facets (as Barrande thinks) or not; from 

 the inferior surface (fig. 5, d) the lenses have fallen out, leaving pits which indicate their 

 size. The posterior corners of the head are rounded off, and they bear, instead of a 

 spine, only a small tubercle (fig. 6), which is placed far inwards. 



The labrum has not yet been found in England, but it is figured in M. de Barrande's 

 plates, and we reproduce it from a Bohemian specimen (fig. 5, e). It is trapezoidal or inverted- 

 pyramidal, half an inch wide by four lines long, straight at the base, where it is much 

 broader than it is long, and the apex is truncate and slightly emarginate. A broad, 

 shallow furrow runs round the end and sides, leaving only a small central convexity of the 

 same shape as the labrum. This convexity is not indented by any lateral furrows. The 

 auricles (see p. 60) are brought to a level with the base, and thus no notch is left between 

 them and the ascending processes, as in those of forms of Cheirurus which most resemble 

 it (see Barrande's plates, xl, fig. 30, and xlii, fig. 19). 



The surface of the head is covered by a fine, close granulation (fig. 6), which occupies 

 also the free cheeks or wings ; it is, therefore, one of the subgeneric distinctions from 

 Cheirurus, in which the cheeks are always pitted or scrobiculate. 



