354 Dr. H. A. Nicholson on the British 



the Graptolithus faccidus described by Hall from the Utica 

 Slate, there can be no doubt ; and in this opinion I am fully 

 borne out by Prof. Harkness, who has examined some of my 

 specimens. Om* British specimens have been placed by Mr. 

 Carruthers under hisi). e/e^ans, which seems to be founded partly 

 upon D. divaricatus, Hall, and partly upon D.fiaccidics. The 

 specimens figured by Mr. Carruthers as D. elegans, and really 

 belonging to D.flaccidus^ are figured upside down (Geol.Mag, 

 vol. V. pi. 5. figs. 8 J, 8 c). 



Our British examples, however, agree with D. flaccidus^ as 

 described and figured by Hall, in the general shape of the 

 frond, in the position of the radicle, in the shape of the cel- 

 lules and in their number to the inch, and, in fact, in every 

 essential respect, except in the fact that the American speci- 

 mens appear to want the small spines which are found oppo- 

 site to the radicle in our form. These, however, are not con- 

 stantly preserved, even in the British specimens ; and even if 

 constantly wanting in the American examples, their absence 

 would not be enough of itself to constitute a specific distinction. 

 From D. divan'catiis, Hall, the present species is distinguished 

 by the fact that the cellules are on the opposite side of the 

 frond to the radicle, the reverse being the case in the former ; 

 whilst the characters of the cellules in the two show several 

 decided points of difference. From D. anceps, Nich., in which 

 the cellules and the radicle hold the same relative position as 

 in D. flaccidus^ the latter is distinguished by the much greater 

 length and tenuity of the stipes, as well as by the different 

 characters of the cellules. 



I have only to add that, in connexion with the fully grown 

 fronds of this species, there often occur numerous young forms 

 in different stages of development, commencing with those 

 which exhibit only one or two cellules on each side of a cen- 

 tral radicle (PI. VII. fig. 6 c). Even in these small forms, 

 however, the three minute spines opposite to the radicle can 

 be recognized. 



Loc. Upper Llandeilo rocks of Dobbs's Linn, and Hart Fell, 

 near Moffat. 



Didymograpsus sextans^ Hall, sp. Fig. 9. 



Graptolithus sextans, Hall (Pal. New York, vol. i. p. 27-3, pi. 74. figs. 3 a-e). 



Dijilograpms (?) sextans, M'Coy (Pal, Foss. part 2, p. 9). 



Graptolithus sextans, Salter (Quart. Journ. (xeol. Roc. vol. v. p. 17, pi. 1. 



fig-. 10). 



Dicranograpstis sextans, Hall (Grapt. Quebec Group, p. 57). 

 Didymoyrapsus sextans, Baily (Characteristic P)ritish Fossils, pi. 9. figs. 

 G a-d). 



Frond consisting of two small stipes, generally from four to 



