644 J. H0PKINS0N AND C. LAPWORTH ON THE GRAPTOLITES OF 



with much, hesitation to this species (Gr. Queb. Group, pi. v. f. 9), 

 it seems more probable that it belongs to this than to D. bifidus, a 

 species occurring in much higher beds. 



Log. Lower Arenig, Road Uchaf, Eamsey Island. 



DlDYMOORAPTTJS PATTJLTTS, Hall, sp. PL XXXIII. figs. 4a-4e. 



1858. Oraptolithus patidus, Hall, Rep. Geol. Surv. Canada for 1857, 



p. 133. 

 1863, Didymograpsus Mrundo, Salter, Quart. Journ. Geol. Soc. vol. 



xix. p. 137, fig. 13/. 

 1866. Graptolithus patulus, Hall, Grapt. Quebec Group, p. 71, pi. i. 



figs. 10-15. 

 1870. Didymograpsus patulus, Nich. Ann. &Mag. Nat. Hist. ser. 4, 



vol. v. p. 340, pi. vii. figs. 1, 1 a. 



Branches long, linear, widening very gradually from their origin to 

 near their extremities, diverging from each other at an angle of 

 180°, or sometimes rather more ; sicula minute ; hydrothecaB 

 20 to 24 to the inch, inclined to the axis at an angle of from 

 45° to 60°, three to four times as long as wide, and with their 

 outer margins free for about one fourth their length ; apertural 

 angle normally 130°, with a concave margin forming with the 

 outer margin curving mucronate denticles. 



The specimens of this species described by Prof. Nicholson from 

 the Skiddaw Slates differ slightly from those from which the above 

 description is drawn up. In these, as in the specimens from the 

 Quebec Group, there are about 24 thecse in the space of an inch 

 (sometimes rather fewer), while in the Skiddaw-Slate specimens the 

 number is from 32 to 34 ; but in the other characters they agree with 

 our specimens. 



As shown in figure 4d, the thecse sometimes lose all the characters 

 by which the species can be determined, varying so greatly in a 

 single branch that, if one part of the branch were separated from the 

 other, the two portions would be referred without a doubt to different 

 species. 



Loo. Middle Arenig, "Whitesand Bay (Salter). Upper Arenig, 

 Llanvirn Quarry, and Porth Hayog, Ramsey Island. 



Didymockrapttjs Nicholsoni, Lapw., sp. nov. PL XXXIII. 

 figs. 5a-5d. 



1868. Didymograpsus serratulus, Nicholson (non Hall), Quart. Journ. 



Geol. Soc. vol. xxiv. p. 136. 

 1870. : Didymograpsus serratidus, Mch. Ann, & Mag. Nat. Hist, ser. 4, 



vol. v. p. 343, pi. vii. figs. 3, da, 35, &c. 



Branches long, usually straight, and somewhat rigid, diverging from 

 a distinct sicula at an angle of about 240°, and having a fairly 

 uniform width of about one twentieth of an inch throughout ; 

 hydrothecse from 25 to 30 to the inch, inclined at an angle of 

 about 30° to the axis of the branch, the concave apertural 



