u- 



\ 



150 BRITISH GRAPTOLITES. 



aperturally, free outer wall with gentle curvature. Apertures slightly 

 introverted, opening within a small excavation, which occupies about one 

 third the width of the stipe. 



Fim. 98^,1, and c.-Bicellograptus Tlie P ^^ ™ tllis S P ecieS is Vei T slender, 



anguiatus, nov. \y n ^ markedly rigid ; the stipes are commonly short 



and very narrow throughout their extent, never 

 exceeding *4 mm. in width. 

 ^WJL 0^* The sicula is conspicuous within the axil, having 



a length of fully 1*5 mm. and passing insensibly 

 /^ upward into the nema. The virgella and lateral 



tf spines are slender, but are usually well exhibited. 



s\ ^A Affinities. — B. anguiatus resembles closely B. 



Forchammeri in its general manner of growth; but 

 it is a much shorter and more slender form, its 

 stipes are more uniform in width throughout their 

 c length, and the characters of its thecre are also 



a. obverse aspect, Literal spines markedly different. 



conspicuous. Enlargement of part 



of pi. xxi, fig. 4. Horizon and Localities. — Upper Glenkiln and 



b. Eeverse aspect. Ibid. 



c. Distal thecoe, showing narrowing at Lower Harttell Shales. 



apertures. Ibid. _, 7 -,-,,- 1T -> t-v-i-i)t- 



S. Scotland : Morroch Bay; Bobb s Lmn. 

 Associates. — B. anguiatus has generally a gregarious habit and is occasionally 

 associated with Oryptog. tricornis ? The best specimens known are in the collection 

 of the Geological Survey of Scotland. 



Group IV. — Type Dicellog. Morrisi. 



Dicellograpti in which the thecas have markedly curved ventral walls, and 

 strongly introverted and introtorted apertural portions. 



Dicellograptus Forchammeri, Geinitz. Plate XXII, figs. 1 a — d. 



1852. Cladograpsus Forchammeri, Geinitz, Die Graptoliten, p. 31, pi. v, figs. 28 — 31. 



1862. Didymograpsus Forchammeri, Bailey, Quart. Journ. Geol. Soc, Dublin, vol. ix, p. 305, pi. iv, fig. 7. 



1871. Dicellograpsus Forchammeri, Hopkinson, Geol. Mag., vol. viii, p. 23, pi. i, fig. 1. 



1876. Dicellograptus Forchammeri, Lap-worth, Cat. West. Scott. Foss., pi. iv, fig. 88. 



1877. Dicellograptus Forchammeri, Lapworth, Grapt. Co. Down, pi. vii, fig. 7. 



Stipes 14 cm. or more in length, generally straight, widening gradually and 

 persistently from their origin up to 1 "2 mm., diverging from a conspicuous 



