1872.] 



>:iCEOLSON' — JI.IGEATIONS OF THE GRAPXOLITES. 



223 



■ Derived from the Skiddaw area. 



Derived from the Welsh Lower Llan- 

 deilo area. 



I- Confined to the Upper Llandeilo. 



B. Species. 



Diplograpsus pristis, His. 

 Climacograpsus teretiusculus, His. 

 ■— bicoruis, Hall. 



Dicranograpsus ramosus, Hall. 



Dicranograpsus formosus, HojiJc. 



Nicholsoni, Hoplc. 



lUdymograpsus anceps, NicJi. 

 Diplograpsus birancronatus, Nick. 



Harknessii, Nich. 



insectiforrais, Nich. 



cometa, Gein. 



acuminatus, Nich. 



Climacograpsus tuberculatus, Nich. 



innotatus, Nich. 



Pleurograpsus linearis, Carr. 

 Rastrites capillaris, CVw'r. 



maximus, Carr. 



Didymograpsus sextans, Hall. 

 — — flaccidus, Hall. 



divaricatus, Hall. 



Diplograpsus Whitfieldi, Hall. 

 Citnograpsus ( Helicograpsus) 



gracilis, Hall. 

 Climacograpsus teretiusculus, His. 

 Diplograpsus angustit'olius, Hall. 



■ vesiculosus, Nich. 



pristis, His. 



palmeus, Barr. 



folium, His. 



tamariscus, Nich. 



Graptolites lobiferus, M'Coi/. 



Sedgwicliii, Portl. 



• Sagittarius, His. 



• tenuis, Portl. 



jS"ilssoni, Barr. 



- — — Clingani, Carr. 

 Bastrites Linnrci, Barr. 



• peregrinus, Barr. 



Betiolites perlatus, Nich, ) 



An analysis of the above Table shows us that out of a total of thirty- 

 six species found in the Upper Llandeilo Shales of Dumfriesshire 

 only four are derived from pre-esistent areas, but these belong to 

 three genera. Thirteen species are exclusively confined to this 

 formation, and are not known' to occur in younger deposits elsewhere, 

 having seemingly died out at the close of the Upper Llandeilo period. 



Five additional species are not known in Britain above this horizon, 

 but e\ddently survived the close of this period, and were able to 

 migrate, as they occur in the Caradoc rocks of North America. It 

 should be noted here that this number might most probably be 

 increased by some species of the genus Graptolites, which almost 

 certainly occur in the Caradoc rocks of America. Owing, however, 

 to Hall's disbelief in the existence of the genus Graptolites as defined 

 by British palaeontologists, this assertion cannot be made positively. 



Sixteen species, or forty-five per cent., including the ancient species 

 Climacograpsus teretiiiseuhcs and Diplograpsus pristis, survive the 



i Confined to the Upper Llandeilo in 

 y Britain, but passing on into tlie 



I Caradoc rocks of America. 



I 



; 



1 



Pass on from the Upper Llandeilo 

 y into the Coniston Mudstoncs of the 

 north of England (Caradoc). 



