4 



BEITISH FOSSILS. 



as in those from Dudley, which often have the lobes as far apart as 

 in Bohemian examples. 



Affinities, — But one species, and of that only a caudal shield, has 

 been described, which at all closely resembles this,— we allude 

 to a species published without name by Dr. Beyrich, from Gott- 

 land, in his second paper (1846, pi. 1. fig. 9) ; it has the side 

 lobes of the tail lengthened out into spines of some length. The 

 terminal joint of the axis too is shorter. There is a second species 

 in Britain, found at Haverfordwest, to which if it were perfect 

 enough, a new name might be applied. It differs from S. mirus 

 in this respect, that the large basal lobes of the glabella are 

 more really tumid, especially outwards, less than their diameter 

 apart, and connected with the body of the glabella by a narrow 

 depressed neck on the inner side, the boundary furrow not com- 

 not completely circumscribing the lobe as in our species. But only 

 a fragment of the head has yet been found, and I may say, that it 

 is singularly like a fragment apparently of this genus lately dis- 

 covered by Captain Strachey in the Silurian rocks of Tibet. There 

 is a species figured by Sars in Oken's Isis, 1835, tab. 9. fig. 8, as the 

 Cal. clavifrons of Dalman, which has a nearly globose glabella with 

 the basal lobes very small ; but it is probably a CheiruruSy and 

 would, we think, be found to possess punctured cheeks. 



History, — That Hisinger s figure of Calym. clavifrons does not 

 represent the species so described by Dalman, though very probably, 

 as Beyrich suggests, it may have been associated under the same 

 name in his collection, has been shown by every author who has 

 since written on the subject ; and the great similarity between it and 

 the species we are describing must be evident to all. Dr. Beyrich 

 supposes it may be the head of the other species we have mentioned 

 above from Gottland ; but, as Hisinger's specimen came from Furu- 

 dal in Dalecarha, this is not certam, and we think we cannot be 

 wrong in referring it to the present cosmopolitan species, of which 

 it is a very good representation. Dr. Be3rrich, when he formed 

 the genus in 1845, had only the head and caudal shield, but these 

 were sufficient to show him the generic distinctions, which we think 

 are now confirmed by characters drawn from the hypostome and 

 thorax rings, since figured by M. Corda and Barrande. 



Professor M'Coy next described the head from Irish specimens, 

 considering it a distinct species from the Bohemian one, but identi- 

 cal with that of Hisinger. His description is very clear, but having 

 found among the Irish specimens considerable variation in the point 

 he marks out as distinctive, viz., the breadth between the lower 



