DICELLOGRAPTUS. 1 L3 



Horizon and Localities. — Upper Hartfell Shales (Dicellog. anc&ps /one). 



8. Scotland. — Dobb's Linn; Ettrick Bridge End; Riskinhope Burn; Black 

 Grain, etc., etc. 



Associates, etc. — This species occurs in fair abundance in the highest zone of the 

 Hartfell Shales in S. Scotland associated with a number of small Diplograptidae, 

 including Dvplog. socialis. 



There are good specimens in the collections of the Geological Survey of Scotland, 

 the Natural History Museum, South Kensington, the Sedgwick Museum, and the 

 private collections of Lapworth and the Authors. 



Group II. — Type Dicellog. divaricatus. 



Dicellograpti in which the thecse have approximately straight vent nil walls, but 

 slightly introverted apertural portions. 



Dicellograptus divaricatus, Hall, Plate XX, figs. 5 a, 5 6. 



1859. Graptolithus divaricatus, Hall, Pal. New York, vol. iii, Suppl., pp. 513, 514, figs. 3, 4. 



1865. Graptolithus divaricatus, Hall, Grapt. Quebec Group, p. 14, fig. 19 (pars). 



1870. Bidymograpsus divaricatus, Nicholson, Ann. Mag. Nat. Hist. [4], vol. v, p. 351, pis. 7, figs. 4, 4 a. 



1875. Dicellograptus Moffatensls, Hopkinson and Lapworth, Quart. Journ. Geol Soc, xxxi, pi. 35, fig. 5 h. 



Stipes 4 cm. or more in length, straight or slightly curved, widening rapidly 



from their origin up to 1 mm., diverging from an inconspicuous sicula at 



angles varying from 270° — 250°. Theca3 twelve to ten in 10 mm., overlapping 



one third to one half their length, free outer walls approximately straight. 



Apertures slightly introverted, opening within a deep and wide excavation, 



occupying nearly half the width of the stipe, and more than one third of the 



free ventral wall of theca. 



Description,. — The stipes vary somewhat in form, being sometimes quite straight 



and rigid, and at other times having a distinct 



Fw. 87 a.-Diceiiogr^tus civ. divan- concave curvature at the proximal end, which 



gradually changes distally to a convex curvature. 

 Their width at the proximal end is about "5 mm., 

 but it increases rapidly within the first 5 mm. to 

 nearly 1 mm., and this width undergoes but little 

 increase. The axillary angle is characteristically 

 a 90°, but may be as small as G0°. 



a. Proximal f e^d x En^.gementof r art ^ ^ Q ^ q{ ^ ^^ ^ rarely visi } )le in tl , e 



axil, but its apertural spine is conspicuous. The 

 lateral spines of th. 1' and th. I 2 are long; a few of the other proximal fchecse 

 also exhibit mesial spines. 



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