340 On the Geological Distribution of the Rhabdophora. 



black shales, apparently of Upper Llandeilo age. In these I 

 have recognized 



Dicranograptus forraosus, Hopk. Climacograptus cselatus ?, Lapw. 



sextans?, Hall. perexcavatus, Lapw. 



Diplograptus foliaceus, Murch. 



During the progress of the Geological Survey of North 

 Wales Mr. Salter detected Graptolites in the deep-seated 

 schists of Tiddyn Dicwm, near Tremadoc. From their appa- 

 rent stratigraphical position he assigned them to the general 

 horizon of the Arenig formation. There can be little doubt, 

 however, that they are actually of Llandeilo age. The speci- 

 mens from this locality preserved in the Jermyn-Street 

 Museum, or figured in the l Geology of North Wales ' *, 

 include Dicranograptus ramosus, Hall, Diplograptus tricornis } 

 Carr., Climacograptus Scharenbergi, Lapw., and G. biconris, 

 Hall. I recognized the same species in a fine collection made 

 by Mr. Hopkinson from this locality in 1873, together with 

 the following additional species : — 



Didymograptus, sp. Diplograptus angustifolius, Hall. 



Glossograptus Hiucksi, Hopk. DiceUograptus sextans (?), Hall. 



Diplograptus dentatus, Brungn. Diplograptus Whitlieldi, Hall. 



Ireland. — The only graptolitiferous strata in Ireland that 

 can with certainty be assigned to the Llandeilo formation 

 are the schists of Bellewston Hill, County Meath, whence 

 Mr. Baily procured Didymograptus Murchisoni, Beck, in 

 association with Diplograptus foliaceus, Murch., and other 



formsf. 



Sweden. — The black shales that overlie the Orthoceras- 

 Limestone of Sweden, and are known as the Dicranograptus- 

 or Middle Graptolite- schists, fall into two tolerably distinct 

 pakeontological groups. The lower group (Murchisoni- or 

 geminus-schists) is marked by the presence of Didymograptus 

 geminuSj His., and several allied species ; and it may there- 

 fore be roughly paralleled with our British Llandeilo. Ac- 

 cording to the most recent researches of Mr. Linnarsson J its 

 lowest beds contain representatives of the British forms 

 Phylhgraptus typus, Hall, Diplograptus Hoplcinsoni, Nich., 

 and Diplograptus tricornis, Carr. These pass up into a 

 group of dark shales with Didymograptus geminus. His. ; and 

 the Llandeilo group is terminated by beds with Glossograptus 

 Hinclcsi, Hopk. With the above forms occur also Diplo- 



* Memoirs Geol. Surv. England aud Wales, vol. iii. pi. xii. 

 t Baily, Journ. Geol. Soc. Dublin, Jan. l^t'iL'. 



J Linnarsson, ' CEfversigt af Vetenskaps-Akademiens Forkandlingar,' 

 1878. 



