154 SILURIAN TRILOBITES. 



limbum ad hoc elevatum ah axe depresso bene separantes. Limbus pauUo convexus, 

 eostatus, margine lato piano sen concavo. Costa axales angustm, 7 — 8; laterales 7 abbre- 

 viatcB, curvce, ad basin duplicate. 



I do not feel quite sure that tliis caudal portion (we possess two specimens only) repre- 

 sents the tail of a Basilicus. It may be a fossil allied to the Ogygia Selicgnii (PI. XVII). 

 But on close examination the axis is so much depressed in front, and is so short, that, as 

 our fossil cannot possibly be that ancient species, it may as well be figured with Basilicus. 



Tail half- elliptic, blunt at the end, the length being to the breadth as 8 to 11. Axis 

 very narrow, not above one third the width of the limb, depressed at its upper portion, 

 where, the axal-furrows being strong here, it is sunk between the convex upper portions 

 of the limb. Behind, the furrows vanish, and the axis is prominent above the more 

 depressed limb : its termination is blunt, and it reaches only two thirds down the tail, 

 or but little more. 



The axis is a little wider in front, then parallel for the rest of its length. The sides, 

 on the contrary, are convex in front and for half their width, and then flat or slightly 

 concave. The seven lateral curved ribs extend only over the convex portion, the ribs 

 being broad and flattened and the furrows narrow. At the base the upper ribs are 

 duplicate, and this is the chief reason for thinking the species may be an Ogygia. 



Locality. — Llandeilo Flags ? Henllan Amgoed, Carmarthenshire. 



AsAPHUs (Basilicus) Powisii, Murchison. PI. XXIII, figs. 2 — 7. 



AsAPHUS Powisii, Murchison. Sil. Syst., t. xxiii, fig. 9 (not a, h), body and tail 

 only, 1837. 



— — Burmeister. Org. Trilob., Ray ed., p. 96, and note: Isofelus 



Powisii, p. 122 (not of Portlock), 1846. 

 IsoTELUS PoTVisii, M'Coy. Pal. Foss. Woodw. Mus., p. 1/0, 1851. 

 AsAPHUS Powisii, Salter. Mem. Geol. Surv., Decade 2, t. iii, p. 5, 1849. 



— — Id. Morris's Catal., 2nd ed., p. 100, 1854. 



— — Id. Siluria, 2nd ed., t. ii, fig. 2, 1859. 



— — Id. App. Ramsay, Geol. N. Wales ; Mem. Geol. Surv., vol. iii, 



p. 312, 1866, pi. XV. 



As. (B.) magnus, sape 6-uncialis, lavis, ovalis, convexus, oculis remotioribus ; caudd axe 

 conico, lateribus vix costatis. Glabella ad frontem rotundata, postice elobata. Caput 

 immarginatum, spinis brevibus. Cauda thorace longior, axe ad basin lato, dein contracto, 

 nisi ad apicem vix elevato, costis 8 — 9 obscuris. Limbus lente declivus sulcis abbreviatis 9, 

 primo soltim pro/undo, reliquis obscuris, margine concavo. 



The original name bestowed by Sir R. I. Murchison is still by common consent 

 retained for this fine fossil, although the author confounded the head of Phacops macroura 

 with the species, as Burmeister first observed in his Ray edition in 1846, and as 

 has been already noticed in our Part I, p. 37. The species is very distinct, and has 



