Distribution of the Rliabdophora. 199 



forms in addition to its characteristic species. It is recog- 

 nizable in the same stratigraphical position and affording the 

 same fossils at Moffat (Barren Mudstones), at Girvan, in 

 County Down, at Rostanga in Scania in the lower part of 

 the Trinucleus-schist, and in Westrogothia. 



9. Zone of Dicellograptus anceps, Nick. — The final zone of 

 the Ordovician system is everywhere characterized by D. 

 anceps in the Moffat area and in the district of Girvan (Drum- 

 muck beds) . According to Dr. Tornquist it. holds the same 

 place and fossils in the Trinucleus-heds of Dalarne. 



Silurian System. 



10. Zone of Diplograptus acuminatus, Nich. — This is the 

 oldest recognizable zone of the Silurian in the Moffat area, 

 where there is no physical line of demarcation at the summit 

 of the Ordovician. In Girvan, where the line of separation 

 is most strongly marked, the same zone is still recognizable. 

 Its pakeontological characters, so far as the Rliabdophora are 

 concerned, are decidedly negative. The Dicellograpta have 

 become extinct, and the Monograpta have not yet appeared. 

 The only forms present are Diprionida. Diplograptus acumi- 

 natus and Climacograptus normalis, Lapw., mark the zone in 

 Moffat and in Girvan. In Sweden it includes the typical 

 beds of the Brachiopod schists, which are similarly marked by 

 an abundance of C. normalis, unaccompanied by members of 

 other Graptolitic families. 



11. Zone of Diplograptus vesiculosus, Nich. — This must be 

 regarded in the light of an introductory zone to the following. 

 In the typical region of Moffat it contains an abundance of 

 the fossil which gives it its name) together with the first 

 forms of Monograptidge (M. tenuis,, Portlock, and M. attenu- 

 ates, Hopk.). It includes the LoAver Pentamerus Limestones 

 of Girvan, and has been identified in the north of Ireland. 



12. Zone of Monograptus gregarius, Lapw. — Whether we 

 have respect to the abundance and variety of its Graptolitic 

 fauna or to the wide geographical range, this zone must be 

 considered the most important in the Llandovery rocks. 

 In the Birkhill area it is capable of division into two sub- 

 zones — the lower marked by the presence of Monograptus 

 triangularis, Harkn., and the upper by the presence of Has- 

 trites peregrinus, Barr. The peculiar species that distinguish 

 the zone may be gathered from a study of Table VII. M, 

 gregarius, Lapw. 7 M. fmbriatus, Nich., Diplograptus physo- 

 phora, Nich., M. leptotheca, Lapw., are especially character- 

 istic. The zone yields the same fossils at Girvan, at Pome- 

 roy and Coalpit Bay in the north of Ireland, in Bornholm, 



