Vol. 52.] GEOLOGY OF THE NEIGHBOURHOOD OF CARMARTHEN. 539 



parallel-sided. Pleura nearly straight, but slightly bent down at 

 the fulcrum, which is situated about half the distance out ; grooved 

 and facetted, also marked beyond the fulcrum by numerous fine 

 stria?. The ends of the pleura are obliquely truncated, but produced 

 posteriorly into short sharp points. 



The pygidium is more than ^ the total length and about ^ broader 

 than long. It is surrounded by a deeply concave striated margin, 

 which is strongly marked off on the inner side by a high convex rim. 

 Axis narrow, tapering gently and ending in a tumid point on the 

 inner rim of the concave margin. It is annulated by six to eight 

 furrows, and the side lobes are marked by a corresponding number 

 of furrows, which reach the inner rim of the margin, where they 

 abruptly terminate. 



This species seems to stand halfway between Ogygia Selwynii, 

 Salt., and Ogygia comdensis, Murch. It differs from 0. Sehvynii 

 in the following respects : — 



(i) The head and tail of 0. Selwynii are equal in length, but in 

 this species the tail is longer than the head. 



(ii) The genal spines of 0. Selwynii are considerably shorter and 

 stouter. 



(iii) The hypostome of 0. Sehvynii is broader in proportion to its 

 length. 



(iv) The margin of the pygidium in 0. Selwynii is broader and 

 less concave, and indistinctly marked off from the rest of the tail. 

 The side furrows are also very short. In the new species the 

 furrows are long and extend quite up to the margin, which is 

 marked off by a high convex rim. 



It differs from 0. comdensis in the following respects : — 



(i) The axis in 0. comdensis is throughout a good deal broader, 

 and that of the tail narrows suddenly, so that its sides are curved. 



(ii) The margin of the pygidium in 0. comdensis is indistinctly 

 marked off and is waved by the lateral furrows, which is never the 

 case in this new species. 



(iii) The genal spines are slightly longer in 0. comdensis. 



(iv) The glabella in 0. comdensis is shorter in proportion to its 

 width. 



(v) The tips of the pleura in 0. comdensis are abruptly truncated, 

 and sometimes bluntly rounded, whereas here we have curving sabre- 

 tips, like those of 0. Buchii, but shorter. 



The feature which marks this species off from other Ogygice is 

 that the margin is raised in a fold towards the inner edge. 



Localities and Horizons : Nant-y-Glasdwr, Cwm Ffrwd, Cwrt Hir, 

 Glan Pibwr, Xant Pwntan, etc., Carmarthen. Tremadoc Slates. — 

 Arenig. 



YI. Conclusion. 



In offering these suggestions with regard to the succession in the 

 neighbourhood of Carmarthen, we feel sure that further evidence 

 will cause many alterations in the boundary-lines which we have 

 drawn between the various series, and we have little doubt that the 



