4 BRITISH FOSSILS. 



the head, the identity might still have been maintained. The hypos- 

 tome of this species was first represented in Sir R. I. Murchison's figures. 

 We have ascertained, by personal inspection, that the Trinudeus Asa- 

 phoides of his work is the young of O. Buchii. Quenstedt, 1837, unfor- 

 tunately got hold of two specimens with seven rings ; whether an accidental 

 variety, or as Burmeister thinks, one occasioned by the slipping of one 

 ring under the others, it is difficult to say. Quenstedt, however, relied 

 on these, and Dalman's 7-ringed specimen of O. dilatata, and asserted the 

 same number for O. Guettardi. But the error in both cases led him 

 to see the generic affinity between these two allied species, and he dis- 

 tinctly says that their union with the typical Asaphi is unjustifiable. 

 Burmeister, in his first edition, set the number of rings right, but con- 

 founded O. 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 dif- 

 ferent species, and figured O. dilatata in Leonhard and Bronn's " Neues 

 Jahrbuch," for 1845. Corda still maintains the error of the seven rings. 



British Localities and Geological Range. LLANDEILO FLAGS only. 

 Not yet known in North Wales ; the localities given for it in the " Geol. 

 Journal," vol. i., p. 20, &c., are erroneous, and were stated to be so in 

 vol. ii., p. 128. It abounds in the distorted slates at Shelve and Hope 

 Mill, Sliropshire (Sir R. I. Murchison) ; Rorrington, Middleton, and 

 Meadowtown, Shropshire ; Builth, Radnorshire ; Llangadoc and Llan- 

 deilo, Caermarthenshire (Geol. Survey Coll.) Haverfordwest ; Muscle- 

 wick Bay, Pembrokeshire (Phillips). Not yet found in Ireland. 



Foreign Distribution. La Couyere, Bain, &c., near Rennes, in the 

 Cote d'or (M. Rouault). In the north of Europe O. dilatata takes its 

 place. 



EXPLANATION OF PLATE VI. 



Fig. 1. Perfect specimen from Builth (the glabella hardly pointed enough in front). 



Fig. 2. Same specimen dissected ; at a the slight ascending furrows which cross the 

 neck segment are seen ; b b, cheeks or wings; c c, fulcral points of the pleurse ; d, tail. 



Fig. 3. Under side of head in front, with the hypostome b attached to the continuous 

 under portion a of the cheeks ; Builth. 



Fig. 4. Young specimen from Builth. 



Fig. 5. Border of the tail, the inflected striate portion rendered wavy by projecting 

 further inwards on each rib. 



Fig. 6. Variety, with the tubercles on the axis strong ; Llandeilo. 



All the specimens in the Geological Survey Collections. 



1849. J. W. SALTEU. 



