Il8 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



species only of Trilobita have occurred in the Scotch Llandeilo rocks, 

 viz. Illcenus Boivmannii, Salteria involuta, and S. primoeva. Ire- 

 land has 5 ; but probably many more will occur. I enumerate them 

 so far as we know them — Acidaspis Jamesii, Ampyx mammillatus, 

 Ogygia Portlockii, Phacops truncato-cauclatus, and JUglina mirabilis. 

 I know no others, although in all the three Llandeilos we have 45 

 species of Crustacea. Shropshire has only yielded 11 species, and 

 these chiefly from the Llandeilo rocks of Shelve : they are all marked 

 species. In the Builth and Llandeilo areas no species occurs below 

 the tuff-beds of the Lower Llandeilo. Pew species of Graptolites 

 are common to the Llandeilo and Arenig rocks of St. David's, al- 

 though here the succession is so complete, and no less than 18 

 species there occur in the Arenig and 6 in the Llandeilo. Only 16 

 species of all groups are common to both formations, although the 

 Arenig fauna numbers 149 and the Llandeilo 175, thus clearly 

 showing the faunal differences. 



Llandeilo beds are known in Merionethshire, Caernarvonshire, 

 Denbighshire, and Anglesey. Fifteen species have been determined 

 from Merioneth ; 13 from Gam, east of Arenig, by far the largest 

 fauna in North Wales. Anglesey from five localities yields 15 

 species and 18 occurrences, or only 3 species for each locality ; 

 Caernarvonshire, from four localities, 17 species (the chief loca- 

 lity, Teddyn-Dicum, has produced 8 species) ; and Craig-y-Glyn, 

 near Llanrhyader in Denbighshire, 6 species. No one can doubt, 

 from the above results, that careful research would greatly add to 

 the faunal value of the Llandeilo rocks of North Wales. Prof. 

 Hughes has lately succeeded in ascertaining the presence of Tre- 

 madoc fossils in Anglesey ; and further search at Garn, east of the 

 Arenigs, could not fail to throw much light upon both the Arenig 

 and Llandeilo faunas, and to substantiate still more the relation 

 between North and South Wales. As yet, out of 13 Garn fossils, 

 we know only 1 Trilobite (Ampyx mammillatus). In Anglesey, 

 near Llanerch-y-medd, out of 5 species collected 3 are characteristic 

 Trilobites — Phacops apiculatus, Asaphus Poivisii, and Galymene cam- 

 brensis. It is the same with Treiorwerth in Anglesey, — clearly 

 showing that a rich harvest of Llandeilo species is yet to be ob- 

 tained in North Wales. 



The elaborate researches of Mr. Lapworth, in Scotland*, into the 

 history of the Rhabdophora of that and other areas, has greatly 

 modified our views respecting their distribution and range. 



The oldest fossiliferous strata known in Scotland are the Grap- 

 tolite shales forming the well-known Moffat series, a group of black 

 shales about 600 feet in thickness, and separated by Mr. Lapworth 

 into three distinct palseontological divisions. The lowest (Lower 

 Moffat or Glenkiln Shales) he determines to be of Upper-Llandeilo 

 age ; the Middle Moffat or Hartfell Shales above he correlates with 

 the Bala group of North Wales " as an attenuated representative ; " 

 and the third or uppermost (the Upper Moffat or Birkhill Shales) 

 represents the Lower Llandovery. This last determination has an 

 * Quart. Journ. Geol. Soc. vol. xxxiv. pp. 240-346. 



