2 



BRITISH FOSSILS. 



we do not know. Eye strongly lunate, long, narrow, smooth, and sup- 

 ported by a very strong fold of the cheek, which forms a sort of lower 

 eyelid, and is most developed in age. Cornea apparently thick. The 

 facial suture in front of the eye runs S-shaped outwards and upwards, 

 turns a little beneath the margin, and then runs straight across above 

 the rostral shield ; it bends out sharply beneath the eye, and cuts the 

 margin beneath the most prominent curve of that organ. Rostral shield 

 a long transverse piece, deeply striate, and overhanging with a sort of 

 pouting lip the attachment of the hypostome. This last piece is yet 

 undiscovered.* Cheeks with rounded angles posteriorly, and curving 

 over the lower side of the head ; they are separated by the wide 

 rostral shield. 



Thorax of 10 segments arched back, especially the forward ones, 

 and having the three lobes just indicated by a very slight furrow where 

 the fulcrum is placed, the subfusiform axis occupying more than two- 

 thirds the entire width. The fulcrum is far outwards, and is formed 

 by a short forward bend of each pleura, which then continues in the 

 general direction, is sharpened anteriorly for rolling, and curves forward 

 at its blunt end ; the foremost pleurse are rapidly shortened, the whole 

 of the cheeks projecting beyond them (plate 3, f. l*a). 



Tail in the young about three-fourths of a hemisphere ; in the adult 

 more than half. The upper corners are truncated and turned down, 

 but there are no indications of the axal lobe. Incurved portion of the 

 tail not broad, but thick, deeply concave, and marked concentrically 

 on both surfaces by elevated lines of dots (pi. 4, f. 10, 10 a). The 

 whole surface of the animal is more or less punctate, and marked with 

 wavy imbricate lines ; they appear to vary very much in number and 

 position, abound near the edges of the head, but less so on its most 

 convex portion ; run across the thorax parallel to the course of the 

 rings, and on the tail are most abundant on its forward margin. On 

 all the articulating surfaces the lines are doubly close, but the puncta 

 absent. On the somewhat depressed space immediately over the fulcral 

 points in the head and thorax-rings, both lines and puncta vanish. 

 These latter, which most probably indicate the bases of short pile, are 

 often wide and deep (pi. 4, f. 3), and are present on the posterior 

 surface of the tail, where the lines are absent. The inferior eyelid 

 (pi. 3, f. 1*^;, if so it may be called, is deeply punctate in our specimen, 

 but without any of the wavy lines. 



Variations. — Though numerous specimens are extant, there are so 

 few perfect ones, that we are not able to detect any considerable variety 

 in the proportions. Certain Dudley specimens appear more elongate. 



* Mr. John Gray of Dudley possesses an entire transverse labrum, with two tubercles, 

 which very likely belongs to it. 



