Vol. 54.] PA UNA OE THE SKIDDAW SLATES. 483 



are inclined at 20°, are in contact with each other for a very small 

 fraction of their length, and their apertures are inclined to the 

 general direction of the stipe at an angle of about 90°. The thecse 

 are about jL. inch long (2-1 mm.) in the mature parts of the stipes, 

 and are about 5 times as long as wide ; their outer wall has 

 commonly a very slight concave curvature. 



Occurrenc e. — Ellergill Beds (?). 



Locality. — Aik lieck, Pooley. 



Genus Dichograptus (Salt.)^ modified. 



Rhabdosoma bilaterally symmetrical. Two branches are developed 

 on either side of the sicula ; these divide dichotomously after a short 

 distance giving rise to four branches of the second order, which are 

 in their tarn capable of dichotomous division at a short distance 

 from the point of the first dichotomy. The stipes of the third order 

 never divide again. A disc may be present or absent. 



DrCHOGKAPTtrS OCTOBKACHIATUS (Hall). 



1858. Grajptolitlius oetohrachiatus, Hall, Geol. Surv. Canada Rep. 1857, p. 122. 



1863. Dicliograpsus aranea, Salt. Quart. Journ. Geol. Soc. vol. xix, p. 137, 

 figs. 9 & 10. 



i863. Dicliograpsus SedgivicTcii, Salt. ihid. fig. 11. 



1865. Gh^ajjtolithus oetohrachiatus, Hall, ' Grapt. of the Quebec Groiip,' Geol. Surv. 

 Canada, dec. 2, p. 96, pi. vii, figs. 1-7 & pi. viii, figs. 1-4. 



1868. Dicliograpsus oetohrachiatus, Nich. Quart. Journ. Geol. Soc. vol. xxiv, p. 129, 

 pi. V, figs. 1 & 2. 



In 1885 Hermann, in his paper 'Die Graptolithenfamilie 

 Dichograptidae,' described D. Sedgwickii, Salt., as a species distinct 

 from D. octobrai hiatus (Hall) since it has curved branches, and the 

 thecae are inclined at a rather lower angle. The curved branching 

 is, I think, only the result of the mode of preservation ; and 

 certainly some specimens, which have their thecae inclined at a high 

 angle and therefore belong to JD. oetohrachiatus, have also appa- 

 rently curved branches. Most of the specimens in the Woodwardian 

 Museum and other collections are preserved with their dorsal side 

 uppermost, and the thecae are not well shown except in a tew 

 cases, and so all details of inclination are obscure. I am inclined 

 to think that the species in question are one and the same, and 

 therefore I include under the name B. oetohrachiatus (Hall) both 

 Salter's species, D. aranea and D. Sedgwickii. 



There are many specimens of D. oetohrachiatus (Hall) in the 

 Woodwardian Museum, and the species seems to have been abundant 

 in the Skiddaw Slates. 



The form is very varied as regards the number of stipes. 

 Perhaps the commonest form is that which has eight stipes of 

 the 3rd order, and from this the species derives its name. Other 

 individuals, agreeing in all respects except the number of stipes, 

 have seven, six, or five stipes. 



