DICELLOGRAPTUS. 159 



associated with Vvplog. dentatus, and it appears to be present at an even lower 

 horizon in S. Wales associated with Didymog. bifidus, Didymog. Nichohoni, 

 Didymog. pakdus, and other forms. 



In S. Scotland and N. Wales it occurs associated with Nemag. gracilis, 

 Didymog. superstes, Dlcellog. sextans, Glimacog. 8charerib&rgi, and other Glenkiln 

 forms, and has also been found in Scotland in the lowest beds of the Hartfell Shales 

 associated with Climacoij. Wilsoni. 



There are specimens in the collections of the Sedgwick Museum, the Natural 

 History Mnsenm, the Geological Survey of Scotland, Lapworth, and the Authors. 



Dicellograptus elegans, Carruthers. Plate XXIII, figs. 2 a — e. 



1868. Bidymograpsus elegans, Carruthers, Geol. Mag., vol. v, p. 129, pi. v, figs. 8 a ami </. 



1871. Dicellograpsiis elegans, Hoplcinson, Geol. Mag., vol. viii, p. 24, pi. 1, figs. 3 a— e,. 



1876. Dicellograptus elegans, Lapworth, Cat. West Scott. Foss., pi. 4, fig. 87. 



1877. Dicellograptus elegans, Lapworth, Grapt. Co. Down, pi. 7, fig. 8. 



Stipes 7 — 10 cm. or more in length, showing pronounced and graceful 

 curvature of their walls, diverging at various angles from a conspicuous 

 sicula, and maintaining an approximately uniform width for the greater 

 part of their length, but narrowing somewhat proximally. Virgella 

 and lateral spines always well developed. Thecre ten to eight in 

 10 mm., overlapping for about one third of their length, and having 

 their free ventral wall strongly curved. Apertures markedly intro- 

 verted and slightly introtorted, opening within a somewhat deep excava- 

 tion, which in profile view occupies approximately half the width of the 

 stipes. 

 Description. — In symmetrical specimens the stipes become nearly parallel to 

 each other in the proximal region, or diverge but slightly with an average 

 distance of 1*5 — 2 mm. between their dorsal walls, the base of the axil being 

 somewhat square; after a short distance, however, they make a decided 

 outward bend with more conspicuous divergence ; they are thus at first 

 straight, next concavely and ultimately convexly curved, though the degree 

 of convexity varies in different specimens. The final direction of growth 

 assumed by the stipes also varies in different individuals, but the proximal double 

 curvature is eminently characteristic of the species. The stipes have an 

 approximately uniform width of "8 — 1 mm., except at their proximal ends, 

 where they are slightly narrower (-6 — *7 mm.). 



The sicula is long and narrow when perfect, and has a length of 2 — 3 mm. 



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