122 F. R. Coivper Reed — Salter's Undescnbed Species. 



cut out by faults ; the beds leading up to the Llandeilo may be 

 looked for in the country east of Ehiw. 



Two points of interest remain to be briefly considered. The 

 highly contorted, crushed, and complicated region to the west of 

 Aberdaron has been spoken of in this paper as " pre-Cambrian," 

 but the writer, in thus expressing the general opinion of geologists, 

 does not thereby intend to exclude the possibility of some of the 

 beds being of later age. The great difference of tectonic arrange- 

 ment on opposite sides of the boundary fault is very striking. In 

 comparison with the intense complication and the metamorphism of 

 the "pre-Cambrian" region the Arenig rocks may be said to be 

 practically undisturbed, and a strong impression of a great difference 

 of age between the two sets of rocks is thus left upon the observer's 

 mind. Direct evidence that this inference is well founded is now 

 afforded by the rock-fragments occurring in the Arenig breccia of 

 the western side of Aberdaron Bay. These fragments consist of 

 pieces of schist, quartz-granulite, etc., unmistakably derived from 

 rocks identical with many of those lying on the other side of the 

 boundary fault, and their condition of alteration corresponds with 

 the present stage of metamorphism of the latter. It is therefore 

 clear that the metamorphism of this " pre-Cambrian " area had been 

 practically completed not later than early Arenig times. 



In this pre-Cambrian region patches of jasper are found associated 

 with green basic igneous rocks. A similar association of rooks has 

 been recently described as occurring along the eastern border of the 

 Highlands of Scotland, where they have been designated the " Jasper 

 and Green-Eock Series." On the grounds of their resemblance to the 

 Arenig radiolarian cherts and lavas of the Southern Uplands of 

 Scotland this Jasper and Green-Eock Series has been considered to 

 be " most probably of Arenig age." ^ Whatever may be the merits 

 of the case as regards the Highland Border rocks, it seems 

 inadmissible to apply the same argument of analogy to the jasper- 

 containing group of the Lleyn, in view of the quite distinct character 

 and altogether different mode of occurrence of the undoubted Arenig 

 rooks near by. 



V. — WOODWARDIAN MUSETJM NOTES : SaLTER's UnDESORIBED 



Species. VI.- 



By F. E. CowPEE, Reed, M.A., F.G.S. 



(PLATE VI.) 



PTEEOPODA. 



CoNULARiA CLAvus, Salter. (PL VI, Figs. 1, la-c.) 



1873. Conularia clavus, Salter, n.sp. : Cat. Camb. Sil. Foss. "Woodw. Mus., p. 163 



(« 878). 

 1891. Conularia clavus, Woods : Cat. Type Foss. "Woodw. Mus., p. 119. 



The original specimen (a 878) is in a very perfect condition and 

 comes from the Wenlock Limestone of Dudley. It also belongs to 



1 G. Barrow : Quart. Journ. Geol. Sec, vol. Ivii (1901), p. 342. 



2 For preyious articles see Geol. Mag., 1901, pp. 5, 106, 246, 355, and 576. 



