DICIIOGRAPTUS. 79 



by the smaller size of its stipes of the first order, and the j^reater width of its main 

 stipes. 



Horizon and LocaUties. — Arenig, Middle Skiddaw Slates (Dichoyrapfns beds). 



Lal-c District : Randal Crag, Skiddaw ; Mire House, Skiddaw ; Carlside Edge, 

 Slape Crags above Hope Hill, Brackenthwaite ; Outerside ; Grisedale Pike. iS. 

 Scotland : Bennane Head, Ballantrae. 



Associates, etc. — D. octohracliiatus occurs in abundance in the Middle Skiddaw 

 Slates of the Lake District associated with Didymograptns hirundo, D. niiidus, 

 D. (jihhcrnlns, D. v-fractus, Tetragraptus, sp. (?), and Lonanogra/ptas Loganl (nonad 

 type). Numerous good specimens are in the collections of the British Museum (Nat. 

 Hist.), theKesAvick Museum, the Woodwardian Museum, and the ])rivate collections 

 of Lap worth, Postlethwaite, and Christophorson. 



Var. Sedgwickii, Salter. Plate X, figs. 3 a, h. 



1863. Diclmjrajtsus SedgivicJcii, Salter, Quart. Journ. Geol. Soc, vol. xix, p. 137, fig. 11. 



In addition to the typical D. octohracliiatus there occurs in the Skiddaw Slates a 

 form which, while agreeing Avith D. octoljrachiatus in the mode of branching and in 

 the number of thecse to the inch, has a decidedly less rigid habit, the stipes being 

 narrower and distinctly flexuous. The thecge, too, are proportionately shorter. 



This is the form described by Salter as a distinct 

 YiG.^^.-Bichograptus odobrachiatus, gpecies Under the title D. SedqwicJdi, but it appears 



var. Sedgwickii, Salter. ^ ./ ' ri 



to US to be better regarded as a variety of D. 

 octohracliiatus. 



Horizon and Locality. — Arenig, Middle Skiddaw 

 Slates. 



Lake District : BraitliAvaite. 



Associates, etc. — The associates of this variety are 

 unknoAvn. The best specimens known to us are in 

 Distal theca.. Enlargement of PI. IX, ^^^^ collection of the Gcological Survcy at Jemiyu 



Street, and in PostlethAvaite's collection. 



Group XL — Type D. separatns. 



Dichograpti Avith slender stipes, having theca' Avhich overlap for a smi 

 fraction of their lemrth. 



11 



