4 



BRITISH FOSSILS. 



genus. In 1845, however, he restored it to Asaphus, though he evi- 

 dently had not observed the characteristic labrum. Burmeister appears 

 not to have been acquainted with the species, since in both editions he 

 confounds it with what we believe to be a specimen of A. heros, and even 

 suggests, in his Appendix, that Murchison's smaller figure might prove 

 to be extenuatus. He notes that it appears anomalous for Asaphus 

 to have such distinct ribs on the tail ; and indeed this peculiarity is one 

 of the indications of its affinity to Ogygia^ which we think confirmed by 

 the course of the facial suture. 



Localities and Geological Position in Britain. — Llandeilo Flags. — 

 Limestone of Wrae, Peebleshire ? (Geol. Society's Coll.). Coniston 

 limestone, Westmoreland ? Craig-y-Glyn, Berwyn Mountains, in Bala 

 limestone (Sedgwick) ; Meadow Town ; Shelve, &c., in the Longmynd, 

 Shropshire ; Carneddau Hill, Builth, Radnorshire [J. W. S.] ; Llandeilo, 

 and many neighbouring localities in Caermarthenshire ; Llampeter 

 Felfry, Pembrokeshire [Murchison] ; Narberth ; Mydrim ; Sholeshook ; 

 Lann Mill, Pembrokeshire (Phillips). It is remarkable that it does not 

 occur in Ireland. 



Foreign Distribution. — It is quoted by Sir R. I. Murchison from 

 Northern Europe [Quart. Geol. Journal], but with the understanding 

 that A. heros, Dalm., was intended. A. marginalis, Hall [Palaiont. 

 New York, pi. 4, his, f. 15], may be the same as our species. 



Explanation of Plate V. 



Fig. 1. Perfect specimen. Llandeilo. (Collection of W. Day, Esq.) 



Fig. 2. Outline of central portion of head, showing the constricted eyelids. Lann Mill. 



Fig. 3. Portion of head, with the base of the eye, a. Llandeilo (Mr. Day's Collection). 



Fig. 3*. Magnified portion of a cast from the same, which would represent the surface 

 of the eye when the smooth cornea is remoTcd. 



Fig. 4. Perfect hypostome, with the upper processes (a a). Lann Mill, 



Fig. 5. Variety of the hypostome, with shorter forks. Golden Grove. 



Fig. 6. Punctate exterior surface of part of hypostome ; the lineated surface is shown 

 in fig. 4. 



Fig. 7, Upper surface of a thorax joint. St. Clears. 



Fig. 8. Under surface of ditto, showing the extent of the incurved portion b, b. 

 Fig. 9. Part of thorax of a large individual, with deep sculpture. Golden Grove, 

 Llandeilo. 



Fig. 10. Tail of young individual. Llandeilo. 



Fig. 11. Incurved part, under side of the tail, bounded by the lines a, a, and deeply 

 indented by the axis. Clog-y-frain. (Sir R. L Murchison's Cabinet.) 



June, 1849. 



J. W. Salter. 



