4 



BRITISH FOSSILS. 



four upper ones are free (or rather much overhanging the margin) ; 

 the remaining two are distinct nearly as far as to the margin, but 

 they there become fiised with those from the opposite side, and 

 extend in a very blunt point beyond the tip of the axis. The 

 uppermost ribs arch strongly outwards, the next less so, and the 

 last pair lie parallel to the axis. 



On the internal cast, the furrows, especially those which bound 

 the axal lobe, are all stronger and deeper, but there is no other 

 difference. Externally the whole surface of the tail is covered with 

 a close scabrosity (see fig. 10). 



Variations. — In the cast from Sholes Hook (fig. 12) the rings on 

 the axis of the tail are effaced down the middle for a broader space, 

 and there are but few of the upper rings continuous across. Our 

 figure in this case does not show the uppermost rings. There are 

 sometimes (fig. 1 1) seven rings on each side of the tail. 



Affinities. — When perfect specimens are obtained, there is no 

 published species with which ours can be confounded. The sub- 

 globular shape of the glabella, with its small tubercles, and the 

 pitted, not tubercular cheeks, will easily distinguish imperfect 

 portions of the head from all other British species. The separated 

 tail, especially internal casts of it, may possibly be confounded with 

 the same portion of E. punctatus, but the want of a central row of 

 tubercles down the axis, and the arched lateral ribs, will enable 

 observers to distinguish it. The other Lower Silurian British 

 species, H. multisegmentatus, Portlock, is diametrically opposed in 

 all its characters ; it has a large coarsely tubercular head, and many- 

 ribbed tail. Nor can the detached tail of our species be confounded 

 with that of Gyhele verrucosa, Dalman, so abundant in company 

 with it, if the four tuberculate lateral ribs of that species be 

 attended to. Ours has six or seven smooth ones. 



History. — We first described this in 1848, in the work above 

 referred to, under the name Cyhele sexcostata. In those figures 

 there was associated with the tail, but only provisionally, a coarsely 

 tubercular head, which occurred so frequently in company with it, 

 that the two might reasonably be supposed to belong to each other- 

 The figure we now give justifies the caution there expressed, for it 

 is the " more clavate form of head rarely occurring,^' which properly 

 belongs to the species ; the head figured in company being, we are 

 now all but certain, that of the C. (Calym.) verrucosa, Dalman, a 

 species which we hope hereafter to illustrate as the British type 

 of the genus Cyhele, Loven. 



It had been previously described in manuscript for Professor Sedg- 



