82 BRTTTSH GRAPTOLTTES. 



10 mm., ontor wall slio'litly ciu'vcmI, inclined o-")", abnnt fonr times as long- 

 as wide, and overlapping- half their length. Apertnral margin straight or 

 very slightly curved, perpendicular. 



The stipes of the first three orders are all very short, but they increase in 

 length with remoteness from the sicula ; thus the stipes of the first order average 

 1 ram. in length, those of the second order 1"() ram., and those of the third order 

 2'1 mm. ; dichotomy is therefore complete within 5 mm. from the point of 

 origin of the stipes. 



The details of the thecse are often obscure and hard to determine, but when 

 the stipes are fully developed they seem to have an average length of nearly 3 mm. 



A disc is frequently present, as in Dichog. ocfohrachiafus. 



Horizon and Localitief^. — Arenig, Middle Skiddaw Slates. 



LaJce District : Outerside ; Barf ; Randal Crag, Skiddaw. 



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

 Britain from the Skiddaw Slates of the Lake District, where poorly preserved 

 specimens are fairly abundant. Many fair examples are in the collection of the 

 British Museum, the Woodwardian Museum, and the Keswick Museum. The best 

 specimens come from Outerside. 



Genus CLONOGRAPTUS, IlaU. 



187;?. Clonograpmts, Hall, compare Nicholson, Ann. Mag. Nat. Hist., ser. 4, vol. xi, p. 138. 



rolypnry bilaterally symmetrical, typically possessing at least thirty-t^vo 



slender uniserial terminal stipes, produced by repeated dichotomous 



division through Didymograptus, Tetragraptus, VicJiograjitns, and Logano- 



gra.pt us stages. 



Thecse simple overlapping tubes. 



The Clonogrnpt.Ks polypary is characterised by the possession of stipes of at 



least five orders. Its nearest allies appear to be Loganograptus and Dichograptus. 



In Loganograptus stipes of more than four orders do not exist, while in Dichograptus 



there are three orders only ; all the earlier stages are short-lived, and nearly equal 



in length. In Cloiiograptns, dichotomy is carried one or several more stages 



beyond the Loganograptus stage (2*), so that examples are known having stipes of 



the sixth order (2"). Again, the distance separating the successive dichotomous 



divisions increases gradually and fairly uniformly from the sicula outwards. It 



is probable that dichotomy was carried farther still, and that stipes of the seventh 



and eighth orders would be found in larger specimens ; it is therefore impossible 



to regard any of the terminal stipes as the main stipes. 



