100 BRITISH GHAPTOLITES. 



purposes of comparison we give a figure of one of the Canadian specimens, in the 

 collection of the Canadian Geological Survey, from Hall's typical locality at the 

 beach below Point Levis. 



Horizon and Localities. — Arenig, Middle Skiddaw Slates (upper beds). 



Lake District : Barf ; Whiteside ; Carlside ; Randal Crag ; Thornship Beck ; 

 Glenderamakin Valley ; Mungrisedale. 



Associates, etc. — P., cf. typns, is not an abundant form in the Skiddaw Slates. 

 It occurs in the upper beds of the Middle Skiddaw Slates associated with F. an- 

 gustifoUtis. It has also been recorded by the Geological Survey of Scotland from 

 the Arenig beds of Bennane Head, but it is doubtful whether the specimens 

 belong to P. tyims. 



The best specimens known to us are in the Woodwardian Museum and the 

 Keswick Museum, in Postlethwaite's collection, and in the Natural History Museum, 

 South Kensington. 



Phyllograptus angustifolius. Hall. Plate XIII, figs. 7 a^. 



1858. Phyllograptus angustifolius. Hall, Greol. Survey Canada Eep., 1867, p. 139. 



1863. Phyllograptus angustifolius, Salter, Quart. Journ. Geol. Soc, vol. xix, p. 137, figs. 7 a, h. 



1865. Phyllograptus angustifolius. Hall, Grrapt. of Quebec Group, p. 125, pi. xvi, figs. 17 — 21. 



1868. Phyllograpsus angustifolius, Nicholson, Quart. Journ Geol. Soc, vol. xxiv, p. 132. 



1898. Phyllograptus angustifolius, EUes, Quart. Journ. Geol. Soc, vol. liv, p. 496. 



Stipes united so as to form an elongate-ovate polypary of variable length and 

 breadth. Thecas eleven to thirteen in 10 mm., inclination increasing 

 steadily towards the distal end, three times as long as wide, free for a 

 small fraction of their length near the aperture. Apertural margins con- 

 cave, with conspicuous denticle, very oblique. 

 Description. — The dimensions of this species vary greatly in different in- 

 dividuals ; the length may be anything below 50 mm., and the width may be as 

 great as 8*7 mm., but is more commonly 4*2 or 4-8 mm. The greatest breadth is 

 generally attained near the base of a long specimen, and, in fact, the polypary is 

 often wider there than at any subsequent point along its length. 



The curvature of the thecae is very similar to that of P., cf. tyf)us, the thecoe 

 at the proximal end coming out nearly horizontally, and then curving slightly 

 back and down ; but the subsequent curvature is far more uniform than is the 

 case with P., cf. ti/pus, where there is an appreciable diminution in the centre of 

 the polypary. 



The form of the thecal apei'ture with its loug denticle is characteristic, there 

 being a greater extension on the lower tliau on the upper side ; this denticle may 

 be one and a half times as long as the width of the theca^ (1 mm.). 



