2 



BRITISH FOSSILS. 



axis of the whole body considerably narrower than the sides. Head 

 finely granular all over, semicircular, without the slightly produced 

 snout, or the long, stout, posterior horns, which are broad at the base, 

 and reach the seventh or eighth thoracic ring. Glabella coarsely 

 tubercular, vv^idened above, more than one-third the width of head, the 

 forehead lobe a transverse rhomb, separated by deep, broad, oblique 

 furrows which nearly meet, from the upper side lobes ; three lateral 

 lobes and neck lobe all nearly equal in width, and together equalling 

 the forehead lobe; the first and second lie straight across, and leave but 

 a narrow ridge down the middle : strong axal furrows separate th& 

 glabella from the triangular cheeks, of the surface of which the large 

 pyramidal eyes occupy a variable proportion ; 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 con- 

 siderable 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 sur- 

 face considerably broader forwards, lenses about 240*, 8 or 10 in a 

 vertical row. In the cast, which represents the crystalline layer behind 

 the lenses, the surface is covered with close-set, circular pits, with 

 narrow distinct borders (Fig. 5) ; in these hollows the moderately convex 

 lenses are set, and in most specimens we see no cornea over them. 

 In two perfectly preserved eyes from Ledbury (Fig. 4), the cornea is, 

 however, present, and contrary to Professor Burmeister's prediction, is 

 distinctly convex over each lens, the intermediate portions being orna- 

 mented 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 fiat, or in other specimens 

 (Fig. 6), it sinks down between them. In Fig. 4 a lens or two is seen 

 to be undeveloped and very small, among other perfect ones. The 

 facial suture exactly circumscribes the glabella in front, falls perpen- 

 dicularly 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 {see 

 Fig. 10 a). The cheek-pieces are united in one (as in all the genus) 

 across the front, and there is no extra piece inserted between them above 

 the hypostome. The latter (Fig. 3) is parabolic, obtusely pointed, the 

 sides a little waved, and the base of attachment extended ; a transverse 

 furrow, within the tip, is connected with a marginal longitudinal one on 

 each side, a pair of lateral strong indentations indicate a second furrow 



* Buckland, Bridgw. Treat,, p. 399, reckons 400. This was probably intended for both 

 eyes. 



