506 BRITISH GRAPTOLITES. 



maximum breadth of 1'8 mm. is reached; cladia numerous, of two, three or 



more generations. Thecee fourteen to ten in 10 nnn., of the general type of 



Monog. spiralis, those of the cladia appearing somewhat more tubular and 



having greater overlap than those of the greater part of the stipe. 



Description. — The polypary often attains considerable size, the stipe with its 



cladia covering several square centimetres. The proximal end of the stipe is 



always spirally (usually helicoidally) enrolled, but the degree of enrolment varies 



with different individuals. 



The place of origin of the first cladium varies considerably, and it often appears 



as if none of the earlier cladia remain attached. In one specimen, however, in 



which all appear to be present and subregularly disposed, they arise as follows: 



First cladium at theca 20 ; second cladium at theca 26 ; third cladium at theca 



Figs. 352 a and b.—CyHograptus Murchi- 32 ; fourtli cladium at tlieca 38 ; fifth cladium at 



sotii, Carruthers. ,, ,_ rni ,^ t it , 



theca 47. Thus the earlier cladia seem to come 

 off sub-regularly every sixth tlieca, and the 

 distance increases somewhat later. There does 

 \ fs/^f not appear to be, however, any precise regularity 

 ^^ Lff ^^^ ^^^^^ respect — a circumstance in harmony with 





the view already mentioned, namely, that the 



W^y^ regularity or irregularity might possibly be de- 



(yj^n termined by the number of individuals remaining 



* . . ^/-r: attached and the number already thrown off. 



'^f^^^r -t^vJ^ fe. i6^ ^^ would, however, seem to be clear that in this 



"^ Vfc^ |%V species at any rate, a considerable number of 



« ^ thecge are developed on the stipe before any new 



a. Portion of the stipe, showing' the type .,..-, i/it \ 



of proximal thecee. Pencerrig, Builth ; individual (cladlUm) ariSeS. 



Wenlock Shales. Coll. Elles. mi i t ^ i j i i 



b. Distal thecBe. Near Newtown. Wenlock I he cladia are commouly souicwhat slcndcr 



Shales. Sedj'wick Museum. j.xi" ■• j • i £ • i • ^^ j. 



° at their origin and widen lairly rapidly up to 



1*8 mm. The first generation of cladia may themselves show the development of 

 a second and even a third generation, which arise in a precisely similar fashion. 



The sicula is usually small and inconspicuous. 



The thecae are slightly more closely set in the initial than in the distal portion 

 of the stipe, but the only visible change they undergo is the tendency to appear 

 tubular rather than sub-triangular in form, a tendency which is doubtless to be 

 correlated with the diminution in curvature and their change in apparent position 

 from the convex to the concave side of the curve. 



Affinities. — The stipe in Cyrtog. Murchisoni shows decided resemblances to that 

 of Monog. spiralis, but is rather more slender and less spirally enrolled, whilst the 

 possession of cladia by the former renders its distinction easy. 



Horizon and Localities. — Wenlock Shales (Denbigh Grits and Flags), (Brathay 

 Flags), (Riccarton Beds), zone of Cyrtog. Murchisoni. 



