BRITISH GRAPTOLITES. 



Scbizograptus tardifurcatus, Elles. Plate VI, fig. 8. 



1898. Schlzograptus tardlfurcatui-, Elles, Quart. Jourii. Geol. Soc, vol. liv, p. 480, fig. 7. 



Stipes rigid, those of first order sliort, those of second order 4 — 5 cm. in length 

 and about 1 mm. in width, constituting the main stipes of the polypary ; 

 from each of these three lateral branches are given off at about 70°, all 

 on the same side. Thecge ten in 10 mm., inclined at about 20°, three times 

 as long as wide ; outer walls slightly curved, overlapping half their length. 

 Apertural margins straight, oblique. 

 Descrij)tion. — The first lateral branch is given off at a distance of 13 mm. 

 from the point of dichotomy, the second at a distance of 8 mm. from the first, 

 the third at a similar distance from the second, etc. Each theca has an average 

 length of al)Out 2 mm. In the type specimen (PL VI, fig. 8) a fourth branch 

 appears to take origin from the opposite side to that of the other three, but this is 

 due to an accident before preservation, as it may not even belong to the polypary. 

 Affinities. — This species differs from S. reticulatus in having more closely set 

 lateral branches, and in these being situated further from the point of dichotomy. 

 Horizon and Locality. — Arenig, Middle Skiddaw Slates (P). 

 Lake District : Carlside Edge. 



Associates. — S. tardifurcatus has not yet been recognised outside the Skiddaw 

 Slates, where it is rare. The best specimens are in Postlethwaite's collection. 

 Its associates are unknown. 



Note. — In the year 18G8 (' Quart. Journ. Geol. Soc.,' vol. xxiv, p. 144, pi. vi, 

 figs. 4 and 5) Nicholson described and figured a fragmentary example of one of the 

 main stipes of a compound Dichograptid, bearing numerous lateral branches on 

 one side only. This fragment he named PleAirograptus vagans, believing it to be an 

 example of a genus to which he had previously given the name of Pleurograptus 

 ('GeoL Mag.,' 1867, voL iv, p. 256). 



AVitli our present knowledge it is evident that the fragment referred to has no 

 generic relationship to Nicholson's original Plcurograptus, which v^as founded on 

 the Leptograptid species Gladograptus linearis of Carruthers. P. vagans belongs 

 clearly to some Dichograptid genus, possibly 8c1iizogra])tiis or Trocliograptus. We 

 have given a figure of Nicholson's original specimen on PI. VI, fig. 9 ; but the 

 characters are so inade(|uate and poorly preserved that it is im})ossible to retain the 

 name as that of a distinct species. 



