Distribution of the Rhabdophora. 335 



III. Upper Arenig. 



Didymograptus bifidus, Hall. Dicellograptus divaricatus ?, Hull. 



affiois, Nich. Climacograptus confertua, Lapw. 



indentatus, Hall. Diplograptus dentatus, Bronrpi. 



Nicliolsoni, Lapw. Glossograptus ciliatus, Emm. 



patulus, Hall. 



Some of the same forms occur in the corresponding Arenig 

 rocks of Merionethshire. In the Jermyn-Street Museum the 

 following forms are labelled as having been collected from the 

 Upper Arenig of Tyobry near Tan-y-Bwylch* : — 



Diplograptus tricornis, Carr. Glossograptus ciliatus, Emm. 



bimucronatus, Nich. Diplograptus foliaceus, Murch. 



Climacograptus confertus, Lapw. angustifolius, Hall. 



The Arenig rocks in the neighbourhood of Shelve yield 

 Rhabdophora in some abundance. From the lowest zones 

 near the Bog Mine I have collected forms of PhyMograptus, 

 Didymograptus , and Trigonograptits. In the Middle Arenig 

 near Shelve church Mr. Hopkinson has detected f Didymo- 

 graptus patulus } Hall, and Clematograptus implicatus, Hopk. 

 I have found some of the same forms at Ladywell Mine, Dis- 

 gwylfa &c. From the Upper Arenig of Ritton Castle I have 

 collected Didymograptus Nicholsoni, Lapw., and D. patulus, 

 '\EIall. Didymograptus cotistrictus, Hall, is not uncommon in 

 similar strata near Snailbeach. 



Lake District. — The Arenig rocks of the Lake District 

 include the Skiddaw Slates of Sedgwick. Little is yet known 

 with certainty with respect to their proper physical and palae- 

 ontological subdivisions. At present it is only possible to 

 regard them, with Prof. Nicholson, as forming two main 

 groups — a lower group of dark flagstones and shales, and an 

 upper group of black shales and mudstoncs. Their Grapto- 

 lites have been made the subjects of special memoirs by Salter 

 and Nicholson ; but the remarkably intertwined character of 

 the two supposed subfaunas renders it more than probable that 

 we have yet much to learn with respect to the systematic 

 places of the several fossiliferous horizons. 



From the Lower Skiddaw Rocks the following species have 

 been collected J : — 



Loganograptus Logani, Half. Schizograptus reticulata, Nich. 



Temnograptus multiplex, Nich. Ctenograptus annulatus, Nich. 



* Collection, Museum, Jermyu Street, case iv. | ,',, Jg, &c. &c. Com- 

 pare also Salter, Mem. Geol. Survey, vol. iii. p. 256 &o, 



t Quart. Juiirn. Geol. Soe. vol. xxxi. p. 636. 



% Nicholson, Ann. & Mag. Nat. Hist., October I860; Quart. Journ. 

 Geol. Soc. vol. xxiv. p. 126 &c. 



