DIDYMOGRAPTUS. 13 



They differ, however, in the general form of tlie polyparj. This closely 

 resembles that of D. iiltidus, the inverted V portion characteristic of D. uniformis 



being much less conspicuous; but this difference 

 Fig. 7.-Didymograptns cf. uniformis, does not lustifv US in Separating off thcsB speciuiens 



sij. nov. J J r o r 



as a distinct variety. 



Up to the present time 1). uniformis has only been 

 recorded from the Skiddaw Slates. The best example 

 !^. <y >^^ yet known is in Postlethwaite's collection, and is 



Proximal end preserved as a cast, ob- regarded as the type Specimen (PI. I, fig. 4). 



verse view. Enlargement of part rr • i r Tt' n • "AT'jn Ol'JJ 



of PI. I, fi«-. 3. Horizon and Jjocalmcs. — Arenig, Middle fekiddaw 



Slates (?). 

 Lake District : Bassenthwaite Sand-beds ; Randal Crag. 



Didymograptus patulus (Hall). Plate I, figs. Sa—c. 



1858. GraptoUihus pedal as. Hall, Rep. Geol. Survey Canada, 1857, p. 131. 



1865. Graptolithus patulus, Hall, " Grapt. of Quebec Group," Geol. Surv. Canada, Canadian Organic 



Remains, dec. 2, p. 71, pi. i, figs. 10 — 15. 

 1868. Non Didymograpsus pattdits, Nicholson, Quart. Journ. Geol. Soc, vol. xxiv, p. 135. 

 1870. Non Didijmocjmpsus patulus, Nicholson {pars), Ann. Mag. Nat. Hist. [4], vol. v, p. 340, 



pi. vii, fig. 1 a. 

 1875. D idymographis patulus, Hopkinson, Quart. Journ. Geol. Soc, vol. xxxi, p. 644, pi. xxxiii, 



figs. 4 a — e. 

 1898. Non Didymograptus patulus, EUes, Quart. Journ. Geol. Soc, vol. liv, p. 504, figs. 22, 23. 

 1901. Non Didymograptus patulus, Toruquist, Lunds Univ. Arssk., Bd. xxxvii, Af. 2, Nr. 5, p. 15, 



pi. ii, figs. 1 — 6. 



Stipes several centimetres in length, widening fairly rapidly from their origin 

 to a maximum width of 2"1 mm., and diverging from a small sicula at about 

 180°. Thecse nine to ten in 10 mm., inclined at a large angle, three to four 

 times as long as wide, free one quarter their length. Apertural margins 

 concave, mucronate, and normal. 

 Descrijption. — The stipes are narrow at their origin, the earliest few thecse being 

 short ; but they lengthen fairly rapidly, and the maximum width of 2*1 mm. is 

 usually attained within the first 12 mm. of the stipe. This width is maintained 

 throughout the length of the stipe, which may attain 5 cm. Near the distal 

 extremities there is again slight diminution in width, owing to the partial develop- 

 ment of the latest thecae. 



The sicula is small ; it is generally rather less than 2 mm. in length. British 

 specimens of this species showing details of the structure of the proximal end are 

 rare, but it would seem that the earliest theca originated close to the apex of the 

 sicula, and that the crossing canal was short and approximately horizontal, so 



