504 MISS G. L. ELLES ON THE GEAPTOLITE [Aug. 1 89 8, 



The sicula is extremely minute, being about -^ inch ('63 mm.) 

 in length. 



Localities. — Aik Beck, Pooley ; recorded by Nicholson from 

 Barf, Carlside Edge, and Ellergill. 



(c) DiDTMOGEAPTUS EXTENSUS (Hall). 



1858. Gr7'aptolithus extensus, Hall, Geol. Surv. Canada Rep. 1857, p. 132. 



1865. Gh'ajitoIWms e.rtensvs, Hall, ' Grapt. of tlie Quebec Group,' Geol. Surv, 

 Canada, dec. 2, p. 80 & pi. ii, figs. 11-16. 



1870. Didymograpsus exfe/isits, Xich. Ann, Mag. 'Nat. Hist. ser. 4, vol. v, 

 p. 341 & pi. vii, tigs. 2&2a, 



1875. JDidymograptus extensus, Lapw, &Hopk, Quart. Journ. Geol. Soc. vol.xxxi, 

 p. 642 & pi, xxxiii, figs, 1 a-d. 



This species does not seem to be at all abundant in the Skiddaw 

 Slates, and all the specimens are so poorly preserved that very few 

 details of structure can be made out. 



The stipes are characteristically slender and iiexuous ; they 

 diverge at a fairly constant angle of 150°, but have a distinct 

 tendency to curve slightly upwards in their more distal portions. 



Some specimens are known whose total length must have been 

 at least 12 inches, and one of about this length from Eandal Crag 

 (Skiddaw) is now in the Woodwardian Museum. 



The stipes increase in width very slowly from their origin up to 

 a maximum which is attained not far from their distal ends ; the 

 decrease near the actual extremity is also gradual. The width 

 of the stipes at their origin is generally about J-q inch ("o mm.) ; 

 this increases up to a maximum of -^ inch (1*58 mm.) in a 

 few species, but more commonly they do not exceed -g^j iuch 

 (I'Oo mm.). 



There are twentj'-four thecae in the space of an inch (about nine 

 or ten in 10 mm.) ; these are long narrow tubes of uniform width, 

 which are 3 times as long as wide in the adult part of the stipes, 

 but probably only twice as long nearer the sicula. The maximum 

 thecal length is ^ inch (2*1 mm.). They are free for one-third 

 of their length distally, but for not more than a half in the proximal 

 parts of the stipes, and are inclined at an angle of about 40°. 



The thecal apertures are concave, and make with the axis of the 

 stipe a variable angle of 100° to 115°. 



Occurrence. — Middle Skiddaw Slates. 



Localities. — Eandal Crag, Skiddaw; below Raven Crag, west 

 of Skiddaw ; Outerside ; Knockmurton, near Lamplugh Cross. 



(Z) DiDYMOGEAPius PATULTJS (Hall). (Eigs. 22 & 23, p. 506.) 



1858. Gh'ciptoUthus patidus, Hall, Geol. Surv. Canada Eep. 1857, p. 131. 



1863. Didymograpsns hirundo. Salt. Quart. Journ. Geol. Soc. vol. xix, p, 137, 

 fig. 13/. 



1865. GraptoJWius patulus, Hall, ' Grapt. of the Quebec Group,' Geol, Surv. 

 Canada, dec. 2, p. 71 & pi. i, figs. 10-15. 



1868, Didymograpsxis patulus, Nich. Quart. Journ. Geol. Soc. vol. xxiv, p. 135. 



1870. Didymograpsus patuhis, Nicb. Ann. Mag, Nat. Hist. ser. 4, vol, v, p. 340 & 

 pi. vii, fig. la, 



1875. DidymograpUis patuhis, Lapw. & Hopk. Quart. Joui'u. Geol. Soc, vol, ixxi, 

 p. 644 & pi, xxxiii, figs, 4 a-e. 



In this species the stipes diverge at a constant angle of 180°, 



