322 BRITISH GRAPTOLITES. 



its variety bimucronatus it differs chiefly in having more remote thecae ; the 

 general plan of construction of the polypary is, however, much the same in both. 



Horizon and Localities. — Llandeilo, Glenkiln Shales and equivalent horizons. 



8. Scotland: Glenkiln Burn; Cairn Ryan; Belcraig, etc. N. Wales: 

 Tiddyndicwm ; Ty Obry. 



Associates, etc. — Ilallog. mitcronatus is an abundant fossil at some localities 

 where there are good exposures of Glenkiln Shales, but as is often the case with 

 Graptolites from that horizon, the specimens are for the most part but poorly 

 preserved. Its common associates are Nemag. gracilis, Dicellog. sextans, and 

 Orthog. Whitfieldi. 



Collections. — Sedgwick Museum, Lapworth, and the Authors. 



Var. inutilis (Hall). Plate XXXIII, figs. 7 a— e. 



1865. Biplograptus inutilis, Hall, G-rapt. of Quebec Group, p. 111. 



1904. Diplograptus inutilis, Ruedemauu, Grapt. of New York.pt. 1, p. 721, pi. xvi, figs. 12 — 13. 



The form described by Hall as Dvplograptus inutilis occurs in the Arenig rocks 



at a few localities only in the British Isles. It 



Fig. 211. — Halloqraptusmucronatus,va,v. -i i 



inutilis (Hail). possesses, however, so many characters m common 



with Hallog. mucronatus that we believe it should be 

 regarded as a variety of that species. 



The polypary is characteristically small, not 

 exceeding 1*5 cm. in length, and the thecas are 

 more closely set, numbering twelve in 10 mm., 

 ^. , , „ , . . , while the spines are shorter and stiff er than in the 



Distal thecoe showing general form. a 



Enlargement of part of PI. XXXIII, tvuical form 

 fig. Id. . . . 



Horizon and Localities. — Arenig, Skiddaw Slates 

 (zones of Didipnog. extensus and D. bifid us). 



Ireland : Sruffaunduff, half a mile west of Bencraff, Connemara. Lake 

 District : Outerside. 8. Wales : Ditch, 100 yards S.E. Kilnpark Farm, Narbeth. 



Associates, etc. — Var. inutilis appears to be as rare a fossil in the British Isles 

 as it is in America. The specimens from which the above description was drawn 

 up were found by Messrs. Muff and Carruthers in the black shales and cherts of 

 Arenig age in the district round Killary Harbour. It occurs there associated 

 with Tetrag. Amii, T. gvadribrachiatus, T. serra, Didi/mog. extensus, and Glossog. 

 acanthus. A single specimen was found in South Wales by the officers of 

 H. M. Geological Survey at a higher horizon associated with Didymog. art its and 

 Amplexog. confertus, and one specimen is known from the Skiddaw Slates. 



Collections. — Geological Survey of England and Wales, Sedgwick Museum, 

 Muff and Carruthers. 





