508 MtSS G. L. ELLES ON THE GHAPlOLlTE [Aug. 189S, 



seen to cut four different cells, and yet the maximum width of the 

 stipe does not exceed -^ inch (1-05 mm.) and is much narrower 

 near the proximal end. 



Occurrence. — Ellergill Beds=Upper Skiddaw Slates. 



Localities. — Aik Beck, Pooley; Thornship Beck ; Ellergill. 



(m) DiDTMo&EAPTFS Y-FRACTTJs, Salt. (Figs. 25-28, pp. 508 & 509.) 



1863. Didymograjpsus V-fractus, Salt. Quart. Journ. Geol. Soc. vol. xix, p. 137, 

 fig. 13 e. 

 1868. Didymograpsus V-fractus, Nicli. ibid. vol. xxiv, p. 134. 



' E,habdosoma consisting of two stipes which, after proceeding 

 downwards from the sicula for a short distance, bend abruptly out- 

 wards, so as to enclose a much more open angle of divergence. 

 The dorsal wall of each stipe is at first convexly and then con- 

 cavely curved. The thecse number thirty-six to the inch (fourteen 

 in 10 mm.); they are inclined 25° to 30°. They are long, narrow 

 tubes, widest at their aperture, and have an apertural angle of 115°. 

 The thecae are in contact for half their length proximally, but for 

 nearly two-thirds of their length in more distal portions of the sti23e.' 



A complete description of this form has never hitherto been 

 given, though it has for a long time been recognized as a well- 

 defined species. There are several good specimens of it, both 

 in Mr. Postlethwaite's collection and in the Woodwardian Museum. 



The general form of the species is as described above, but the 

 examination of a number of specimens reveals considerable variation 



Pig. 2b. — Didymograptus V-fractus, //-o???. Barf ; 

 coll. Woodwardian Museum, 



Nat. size. 

 [A = reverse aspect; B = obverse aspect.] 



from the typical form, especially as regards the length of the 

 V-part, and the direction taken b^^ che stipes after the abrupt beud. 

 In some cases the Y-shaped part is narrow and rather long, in 

 others it is small and the branches after the bend are exceedingly 

 long; while in others again the initial angle of divergence is 

 greater, and the change in direction less abrupt. Some forms indeed 

 approach very nearly to Tullberg's Didymograptus vacillans, but 

 the stipes of that species are of a more uniform width than in 

 D. V-fractus. 



Notes on Structure. — The sicula is long and narrow; it 

 attains a length of ^g- inch (1-58 mm.) exclusive of the prolongation 



