﻿us 



SILURIAN TRILOBITES. 



Britannici IchnograpTdd (1699), where he again says the specimen represents only the 

 sceleton of a sole fish, and wants the tail; and he marvels that the ' Piscis Icon' should 

 be raised above the surface of the stone, ' ac si verus piscis esset.' It is curious that 

 Brongniart should have placed this species in his heterogeneous group Asopl/us, at the very 

 time he was founding Ot/ygia, as he appears to have recognised the latter genus more by 

 its marked habit than by any positive characters ; and the principal species, 0. Guettardi, 

 turns out to be an Jsaphus. He probably meant to unite A. dilatatus with A. Buchii. 

 Dalman distinguished them, but with doubt, in 182G, and gave a figure of the Norwegian 

 fossil from a plaster cast; and had not Sars, in 1835, given a complete description and 

 a good figure of the head, the identity might still have been maintained. But, though 

 often quoted, 0. dilatata does not occur in Britain. Dalman described a specimen of 

 it with seven body-segments ; and Prof. Quenstedt, in 1837, two specimens of 0. Buchii 

 with seven rings ; whether an accidental variety, or, as Burmeister thinks, occasioned by 

 the slipping of one ring under the others, it is difficult to say. Quenstedt, however, 

 relied on these and Dalman's seven-ringed specimen of 0. dilatata, and asserted the 

 same number for Asaphus (0.) Guettardi. But the error in both cases led him to see 

 the generic affinity between the two former species, and he distinctly says that their 

 union with the typical Asap/ii is unjustifiable. Burmeister, in his first edition, set the 

 number of rings right, but confounded 0. dilatata, which Sars had well distinguished 

 in Oken's ' Isis' (1835), with our species; and adhered to this view in the Ray edition 

 (1846). Emmerich had, in the mean time, spoken of them as different species, and figured 

 0. dilatata in Leonhard and Bronn's ' Neues Jahrbuch' for 1845;" and Corda, in his 

 notoriously incorrect work, in 1847, maintained the error of the seven rings, after every- 

 body else had clearly understood that all the Asaplii and Ogygia? had eight segments. 



Localities. — Llandeilo Flags only. Shelve and Hope Mill, Shropshire ; Rorington, 

 Middleton, and Meadowtown, Shropshire ; Builth, Radnorshire ; Llangadoc and Llandeilo, 

 Caermarthenshire ; near Haverfordwest; Musclewick Bay, Pembrokeshire ; and Abereiddy 

 Bay, Cardiganshire, where it is abundant. 



It is not known in any foreign country ; nor, indeed (though often so quoted), has 

 it been found out of South Wales. It must be esteemed an extremely local and very 

 abundant species, and not very variable, except as regards those differences referable 

 to sex. 



