a Family of Graptolites. 15 



8. Didymograptus superstes, Lapw. 



Lower Bala, Ireland ; doubtfully near Albany, N.Y. 



9. Didymograptus nitidus (Hall), Nich., Ether., Lapw. 



Oraptolithus nitidus, Hall. 



Quebec Group, Canada ; Skiddaw Slates ; Arenig, Australia ; 

 doubtfully in Phyllograptus-shales, Norway. 



10. Didymograptus suecicus, Tullb., Lapw., Brogger. 

 Tetragraptus-zone, Skane ; Phyllograptus-shales, Norway ? 



b. Type Didymograptus Mnrchisoni, Beck. 



11. Didymograptus Murchisoni (Beck), Baily, Tornquist, Hopk., 

 Nick., Trom. and Lebesc, Lapw., Tullb. 



Gmptolithns Murchisoni, Beck, Boeck. 

 Prionotus (?) geminus, His. 

 Graptolithus geminus, Scharenb., Kjerulf. 

 Didymoyraptus furcillatus, Hopk. and Lapw. 



Angle of divergence about 40°. 



Lower Llandeilo, Wales; Didymograptus-Murchisoni zone (Et. 4.) 

 Norway, Skane, France, Portugal. 



12. Didymograptus indentus (Hall), Hopk. and Lapw., Brogger, 

 Tullb. 



Quebec Group, Canada ; Upper Arenig, Wales ; Pltyllograptus- 

 shales, Norway ; zone with Tetragraptus, Skane. 



13. Didymograptus indentus, var. nanus, Lapw. and Hopk. 



D. geminus, Nich. 



Skiddaw slates, N. England ; Upper Arenig, Wales ; Lower and 

 Middle Llandeilo, Wales. 



14. Didymograptus minutus, Tornquist, Lapw. 

 Phyllograptus-slvdles, Dalecarlia. 



15. Didymograptus bifidus (Hall), Nich., Hopk., and Lapw., 

 Brogger, Tullb. 



Angle of divergence 15°-20°. 



Quebec Group, Canada ; Skiddaw Slates, N. England ; Upper 

 Arenig, Wales. A somewhat divergent form in Phyllograjitus-sk&ies, 

 Norway ; zone with PhyUograptus typus, Skane ; Upper Arenig, 

 N. England. 



c. Type Didymograptus fascicidatus, Nich. 



16. Didymograptus fascicidatus, Nich., Lapw. 

 Upper part of Skiddaw Slates. 



17. Didymograptus arcuatus (Hall), Nich. 



With a process opposite to the sicula. Quebec Group, Canada. 



d. Type Didymograptus permatulus (Hall). 



18. Didymograptus pennatulus (Hall), Hopk. and Lapw. 

 Angle of divergence nearly 180° (Hall). 



Quebec Group, Canada ; Lower Arenig, Wales. 



19. Didymograptus sparsus, Hopk., Lapw. 

 Lower Arenig, Wales. 



20. Didymograptus gibberidus, Nich., Lapw. 

 Lower part of Skiddaw Slates, N. England. 



