118 



BRITISH GRAPTOLITES. 



and are especially conspicuous in the proximal region, where the amount of overlap 

 is reduced to a minimum, and where the apertures occupy nearly the entire width 

 of the stipe. In the more distal regions, however, the amount of overlap increases 

 up to one-half, the thecae have a length of 2 mm., and the thecal apertures only occupy 

 one-third of the total width of the stipe. 



Affinities. — Leptograptus ascendens approaches in general form the two allied 

 species of Dicellograptus, D. intortus and D. caduceus. It differs from either of 

 these in the character of the thecae, which belong clearly to the Leptograptus rather 

 than to the Dicellograptus type. From all other Leptograpti it may be distinguished 

 by its scandent form. 



Horizon and Localities. — Glenkiln Shales (zone of Nemag. [Coenog.~\ gracilis). 



8. Scotland: Foot of Hawkwood Burn, Abington ; Pulmaddy Burn, near 

 Carsphairn. 



Associates, etc. — This species has as yet only been found in the Glenkiln Shales of 

 S. Scotland, where it occurs associated with such typical forms as Nemag. (Goenog.) 

 gracilis, Dicellog. sextans, and Didymog. superstes. 



The type specimens are in the collection of the Geological Survey of Scotland. 



Specific Characters of Forms belonging to the Genus Leptograptus. 





* 











L. 



L. 





z. 



l. 



L. 





■"•'"""" 



var. 



var. 



var. 



var. 



capillar it. 



validm. 



var. 



graiidi/. 



latin. 



a,cenden.. 







tpinifer. 



maciUntias 



macer. 



arcuatus. 







ineitut. 









( iharacter of stipes . 



Graceful 



Straight 



Rigid or 



Narrow, 



Slightly 



Slender 



Some- 



Slender 



Rigid, 



Mark- 



Strongly 





double 



or with 



stiffly 



with 



sigmoid 



and 



what 



and 



or very 



edly 



curved 





curva- 



irregulai 



curved 



slight 



curva- 



mark- 



rigid or 



some- 



slightly rigid and 



so as to 





ture in 



curva- 





and vari- 



ture 



edly sig- 



but very 



what 



flexed, widen- 



cross 





proximal 



ture 





able cur- 





moid 



slightly 



rigid 



wide 1 ing 



eacli 





region 







vature 





curva- 



flexed", 





through- rapidly 



other. 





ulti- 











ture 



wide at 





out 









mately 













origin 













hori- 

























zontal 























Maximum width of 



1 mm. 



0-8—1 



1 mm. 



0G mm. 



1 mm. 



05 mm. 



1 mm. 



0'7 mm. 



15 mm. 



14 mm. 



1 mm. 



stipes 





mm. 





















Length of sicula . 



1-5— 1-6 



mm. 



2 mm. 



1-6—2 

 mm. 



2 mm. 



2 mm. 



2 mm. 



1'5 mm. 



2 mm. 



15— 16 

 mm. 



1-5 mm. 



12 mm. 



No. of thecse in 



10-8 



9—10 



9-8 



6 



7-8 



8—10 



10—11 



10—8 



10—9 



12—14 



10—9. 



10 mm. 

























Inclination 



15° 



15° 



15 ° 



Same as 

 typical 

 species 



Same as 

 typical 

 species 



— 



10° 



12° 



10° 



10°— 25°. 





( Overlap . 



i-i 



i 



h- J 



Ditto. 



Ditto. 



\ 



h—l 



i~i 



1 



* 



0— 1. 



