314 BRITISH GRAPTOLITES. 



Glossograptus acanthus, sp. no v. Plate XXXIII, figs. 4 a — c. 



Polypary sub-fusiform, having a length of about 2*5 cm. or more, and widening 

 quickly from 1*5 mm. to a maximum breadth of 4 mm., then diminishing distally. 

 Sicula only observed in its apertural region. Thecas ten in 10 mm. ; apertural 

 margins distinctly everted, with robust, rigid, slightly curved apertural spines 

 nearly equal in length to breadth of polypary ; septal spines ? robust, stiff. 



Description. — The polypary of G. acanthus is characterised by its breadth, sub- 

 fusiform outline, and robust spines. These spines 



Figs. 208 a and b. — Glossograptus .. -. . . , -r> • , • ■, 



acanthus, sp. nov. appear much broader than m any other British 



species, the denticle being distinctly elongated and 

 its thickened margins merging insensibly into the 

 base of the spine itself. In the proximal region of 

 the polypary they usually extend mainly in a down- 

 ward direction, but they gradually become more or 

 less horizontal, and in the distal region they have 

 « '* a somewhat ascending direction. In this form we 



a - P th^pini Sh Flla^;So^ ™™ l J see more th ™ °" e of tlie tw o apertural spines 

 , of pi. xxxiii, fig. 4 o. belonging to each theca. The septal spines are not 



b. Proximal end, thecse somewhat dis- ° ° l * 



torted. Enlargement of part of known with Certainty. 

 PI. XXXIII, fig. 4 c. _ # J 



The sicula, which is only seen in its apertural 

 region, appears to extend free beyond the end of the polypary. It is provided 

 with two stout spines. 



The sub-fusiform shape of the polypary and the disposition of the spines give 

 to this species a more Phyllograptid appearance than that of any of its British 

 congeners. 



Affinities. — G. acanthus somewhat resembles G. echinatus, Ruedemann, but differs 

 in its more fusiform shape and in the disposition and more robust nature of its spines. 



Horizon and Localities. — Arenig (zones of Didymog. bifid us and I), extensus). 

 Skiddaw Slates (Ellergill beds). 



Lalee District .- Thornship Beck. S. Wales : Llanvirn Quarry, near St. David's. 

 N. Wales : Nant-yr-Orlof, Arenig. Ireland : Sruffaunduff, half a mile W. of 

 summit of Bencraff, Connemara ; W. end of Rossroe Peninsula, between the 

 Killaries ; Roadside, N. end of Doolough, Co. Mayo. 



Associates, etc. — Glossog. acanthus occurs in Wales and the Lake District 

 associated with Didymog. bifidus, and in Ireland it has been found by Messrs. Muff 

 and Carruthers on a somewhat lower horizon (zone of Didymog. extensus), asso- 

 ciated with Tetrag. quadribracliiatus, T. Amii, Hallog. mucronatus var. inutilis, 

 Phyllograptus, etc. 



Collections.— Sedgwick Museum, Muff and Carruthers, Fearnsides. 



