496 Miss a. l. elles o^ the graftolite [Aug. 1898, 



abundant in the Middle Skiddaw Slates (upper part) at several 

 localities. 



Localities. — Barf ; Whiteside ; Carlside ; east of Dodd Wood ; 

 Randal Crag ; Glenderamakin Valley ; Mungrisedale. 



(6) Phyllograptus angustifolius, Hall. 



1858. Fhyllograptus angustifolius, Hall, Geol. Surv. Canada Rep. 1857, p. 139. 

 1865. Fhyllograptus angusUfolius, Hall, ' Grapt. of the Quebec Group,' Geol. Surv. 

 Canada, dec. 2, p. 125 & pi. xvi, figs. 17-21. 



1868. Fhyllograpsus angustifolius, Nich. Quart. Journ. Geol. Soc. vol. xxiv, p. 132. 



This species, like that just described, has a varied form, but it 

 is never broadly ovate. 



The curvature of the thecse is very similar to that of Ph. typus, in 

 so far as at the proximal end the thecse come out nearly horizontally 

 and then curve slightly back and down ; but the subsequent curva- 

 ture is far more uniform than is the case with Fh. typus^ where 

 there is an appreciable diminution in the centre of the rhabdosoma. 

 The inclination of the thecae increases steadily towards the distal 

 end. The thecae are more numerous than in Ph. typus : there are 

 generally thirty in the space of an inch, though the number maybe 

 as low as twenty-eight or as high as thirty-two (eleven to thirteen 

 in 10 mm.). 



The form of the aperture with its long denticle is characteristic, 

 there being a greater extension on the lower than on the upper 

 side. The denticle may be as much as 1^ times the width of the 

 thecae. 



The dimensions of the species vary greatly in different indi- 

 viduals ; the length may be anything up to 2 inches (50'7 mm.), and 

 the width may be as great as -J- inch (8*7 mm.), but is more 

 commonly i or y^g inch (4-2 or 4*76 mm.). 



In broader forms the species approaches Phyllograptus typus^ 

 but can be distinguished by (1) the form of the cell-aperture ; 

 (2) the greater number of cells in a given unit of length. 



The greatest width is often attained near the base of a long 

 specimen, and, in fact, the rhabdosoma is often wider at this point 

 than at any subsequent point along its length. 



Occurrence. — The species appears to be very abundant in the 

 Middle Skiddaw Slates ; it occurs on the same slabs as Phyllogyxiptus 

 typus, Hall, Ph. Anna, Hall, Tetragraptus Bigsbyi (Hall), Didymo- 

 graptus nitidus (Hall), and Dichograptus octobrachiatus (Hall). 



Localities. — Barf; Carlside; Whiteside; Randal Crag; Bassen- 

 thwaite Sand-beds : Knott Head, Whinlatter. 



J 



Genus Didymograptus, M^Coy. 



{e) Didymograptus gibberultjs, Nich. (Figs. 17 & 18, pp. 498, 499.) 



1853. ? I>idymograpsus caduceus, Salt, (jpars) Quart. Joui-n. Geol. Soc. vol. ix, 

 p. 87, fig. 1 a. 



1863. ? Didymograpsus caduceus, Salt. ihid. vol. xix, p. 138, fig. (p. 137) 13 a, 6 ? 



1875. Didymograptus gibbet'ulus, Nich. Ann. Mag. Nat. Hist. ser. 4, vol. 'xvi, 

 p. 271 & pi. vii. tigs. 3, 3a & 3b. 



