2 



BRITISH FOSSILS. 



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 circumscribed, 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 communication with the body of the glabella (fig. 3, a, 

 11 a). Above these lobes on each side are two faint impressed lines 

 which represent the upper furrows (in fig. 4) ; of these (a) 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 (b) at an equal distance in advance of 

 it towards the front. The cheeks are small in comparison with the 

 glabella, and hang vertically from its sides (fig. 4, 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 from it out- 

 wards, and reaches the exterior margin which it cuts obliquely a 

 little in front of the posterior angle, as at fig. 3, c ; 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. 4, d). Each free cheek is hatchet-shaped, and the 

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

 of the crust, h, 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 ; the surface 

 is therefore left blank (fig. 6, a) ; from the inferior surface, h, the 

 lenses have fallen out, leaving pits which indicate their size. The 

 posterior corners of the head are rounded oflf and contracted to a 

 less width than the free cheeks, and they bear instead of a spine, 

 only a small tubercle (fig. 3, d), which is placed far inwards. 



The hypostome has not yet been found in England, but it is 

 figured in M. de Barrande's* plates. It is subtrigonal, straight at 

 the base, where it is much broader than it is long, and the apex is 



* If this figure be as complete as M. de Barrande's figures usually are, there is no lateral 

 notch nor any visible ascending processes. M. Corda's figure, however, exhibits a narrow 

 rim at the base, with a small lateral process on each side. The notch would then exist 

 between the lateral border or wing (fliigel), and these small processes and the resemblance 

 to Cheirurus, in other respects so closely allied, would be more complete. 



