DICELLOGRAPTUS. 155 



W. of Douglas, Peebles; Cairn Ryan, etc. Crirvan Area: Benan Burn, etc. 

 Ireland: Tramore Bay, Co. Waterford; Ballymoney, Co. Waterford; Six Mile 

 Bridge, Co. Clare. 



Associates, etc.—D. sextans is a very abundant fossil in the graptolitic facies of 

 the Llandeilo beds (Glenkiln Shales). It occurs associated with Didymog. 

 superstes, JSfemag. gracilis, Climacog. Scharenbergi, Vvplog. Whitfieldi, and other 

 forms. It is but rarely well preserved in spite of its abundance. Fairly 

 good specimens are in the collections of the Sedgwick Museum, the Geological 

 Survey of Scotland, British Museum of Natural History, and the private 

 collections of Lapworth and the Authors. 



Var. exilis, var. no v. Plate XXI, figs. 2 a — d. 



In addition to the typical Dicellog. sextans, there 

 var - is also found on the same horizon a form which 

 agrees with it in all its characters, except that it is 

 far more slender, being only about half the breadth 

 of the true I), sextans. Owing to its common occur- 

 rence, this form seems to be worthy of varietal dis- 



dmal end. Enlargement of part tmctlOU. 



of pi. xxi, fig. 2 a. j£ g i 10r i Z011 an d associates are those of D. sextans 



itself. 



Dicellograptus Morrisi, Hopkinson. Plate XXI, figs. G a— d. 



1867. Didymograpsus flaccidus, Nicholson, Geol. Mag-., iv, p. 110, pi. viii, figs. 1 — 3. 



1868. Bidymograpsus elegans, Carruthers (pars), Geol. Mag., vol. v, pi. v, figs. 8b and 8 c. 

 1871. Bicellograpsus Morrisi, Hopkinson, Geol. Mag., viii, p. 24, pi. i, figs. 2 a — h. 



1876. Bicellograptus Morrisi, Lapworth, Cat. West. Scott. Foss., pi. iv, fig. 85. 



1877. Bicellograptus Morrisi, Lapworth, Grapt. Co. Down, pi. vii, fig. 6. 



Stipes 10 — 12 cm. or more in length, robust and somewhat flexed, ultimately 

 attaining a width of 1"3 mm., diverging at 320° from a small but con- 

 spicuous sicula ; virgella and lateral spines short and thick. Axil somewhat 

 rounded. Thecae twelve to nine in 10 mm., overlapping one third to one half 

 their length ; free part of outer wall curved. Apertural margin introverted 

 and introtorted, opening within a pouch-shaped excavation which occupies 

 one half to one third the width of the stipe. 



Description. — The stipes, which are frequently very long, have as a rule a very 

 gentle convex curvature throughout, though occasionally there are indications of a 



