94 BRITISH GRAPTOLITES. 



siciila is very slender, and as a consequence the stipe is frequently found In^oken at 

 this point. The length of a mature theca is about 2*5 mm. 



Affinities. — Azj/gograptus Lapworthi resembles some examples of Az. Hicksii in 

 tlie curvature of the stipe, but differs in having shorter and more closely set thecse. 

 From the other two species — Az. coehhs and Az. siiecicus — it can be easily separated 

 by the curvature of its stipe and the position on the sicula at which the stipe 

 originates. 



Horizon and Localitij. — Arenig, Middle Skiddaw Slates {Diclior/rapfas beds). 



Lal-e Didrid : Hodgson How Quarry, near Portinscale. 



Associates, etc. — Up to the present time this species has only been recorded 

 from the Skiddaw Slates, where it is very abundant at a certain horizon. It has 

 not been found associated with any other forms. Several good specimens are in 

 the collections of the Keswick Natural History Museum, the Woodwardian 

 Museum, the British Museum, and in the private collections of Lapworth, 

 Nicholson, Postlethwaite, and the authors. 



Azygograptus Hicksii (Hopkinson sp.). Plate XIII, figs. 2 a — e. 



1875. Tetrcujraptus Hicksii, Hopkinsou, Quart. Joum. Geol. Soc, vol. xxxi, p. G51, pi. xxxiii, figs. 

 12 a-d. 



Stipe considerably curved, 2-5 to 7'5 cm. in length, slender at origin, but quickly 

 attaining a maximum width of about Vo mm., originating from a con- 

 spicuous sicula at a little distance above its aperture. Thecte four to five in 

 10 mm., very long tubes, three times as long as wnde, widening gradually in 

 the direction of their apertures, with concavely curved outer walls ; inclina- 

 tion 10° to 15°, overlap increasing from mere contact to one third tlieii' 

 length. Apertural margins slightly concave, oblique. 

 Descrijjtion. — The stipe is slender at its origin, being about 'O mm. in breadth, 

 but it widens rajjidly up to about I'O nun., and thereafter no further increase takes 

 ])lace even in stipes having a length of 7"0 cm. 



The sicula is conspicuous but narrow ; it has a 

 length of 1-7 mm. The first theca originates 

 approximately in the centre of the sicula, grows 

 slightly downward, and then sometimes curves out- 

 ward in a manner recaUing that of Az. Lapworthi ; 

 but the amount of curvature of the stipe varies con- 

 siderably in different individuals, though it is always 

 convex. 



The theccU are about o mm. in length ; they are 

 inclined from 10° to 15°. In the proximal region of 



Fio. 



55 a.- 



Hopkinson. 



Hicksii, 





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