476 MISS G. L. ELLES ON THE GEAPTOLITE [-A.Ug. 1898, 



to two stipes of the 3rd order, one of which persists, and one is 

 again dichotomously divided : 



The definition of Loganograptus should run thus : — 

 Ehabdosoma typically symmetrical ; short branches of the 1st 

 order arise on either side of the sicula, and these, by repeated 

 dichotomous division, give rise to a form whose branches vary in 



number 6-32 ? Dichotomy never takes place less than 3 times. 



Disc may be present or absent. 



LOGANOGRAPTFS LoGANI, Hall. 



1858. GraptoUthus Logani, Hall, Geol. Surv. Canada Rep. 1857, p. 115. 



1865. Grraptolithus Logani, Hall, ' Grapt. of Quebec Group,' Geol. Surv.- Canada, 

 dec. 2, p. 100 & pi. ix, figs. 1-9. 



1867. Loqanograptus Logani, Hall, ' Introd. Study Graptolitidse,' N.Y. State Cab, 

 Nat. Hist. 20th Ann. Rep. p. 226. 



This species is abundant in the Skiddaw Slates, but none of 

 the specimens that I have seen possess more than sixteen stipes ; 

 and there are specimens with twelve, ten, nine, eight, and seven 

 stipes respectively. All dichotomy takes place within -g- inch 

 (4*23 mm.) from the point of origin of the earliest stipes. 



The stipes of the 1st order are about -^ inch long (1*05 mm.), 

 those of the 2nd order y^- inch (1'5 mm.), and those of the 3rd 

 order -^^ inch (2'1 mm.), while those of the 4th order may be 

 2 inches or more in length (50*8 mm.). These stipes are narrow 

 at their origin, but widen to a maximum at jL incli (1-5 ram.). 



The thecse are twenty-two to twenty -four in the inch (eight to nine 

 in 10 mm.), they are inclined at 35°, are free for about half their 

 length, and have their apertures placed almost perpendicularly to 

 the general direction of the stipe. 



One specimen from Oaterside now in the British Museum (Xat. 

 Hist.) has sixteen stipes, and is figured by Nicholson.^ 



Occurrence. — Middle Skiddaw Slates. 



Localities. — Randal Crag, Skiddaw ; Barf; Outerside. 



Genus Trichoyraptus^ Nich. 



Teichogeaptus feagtlis, Nich. 



1869. Lichograpsus fragilis, Nicb. Ann. Mag. Nat. Hist. ser. 4, vol. iv, p. 232 & 

 pi. xi, figs. 1-3. 



1876. Trichograptus fragilis, Nich. Geol. Mag. dec. 2, vol. iii, p. 248. 



The only specimens of this delicate little species known to me are 

 the types which are in the British Museum (Nat. Hist.). The 

 species is very fragile, and is peculiar, in that of the four stipes 

 of the 2nd order produced as a result of the dichotomy of the 

 earliest stipes, the two upper ones are alone capable of further sub- 

 division, the other two persisting as single stipes. 



Nicholson regards the branches given off by the two upper stipes 

 as lateral, and he therefore refers them all to the same order of 

 branching — the 3rd order. 



1 ' Monograph of the British araptolitidse,' 1872, p. 109, fig. 52 c. 



