230 PROCEEDINGS OP THE GEOLOaiCAL SOCIETT. [Feb. 21, 



series of Bohemia, viz. Etage D, at the summit of the Lower Silurian 

 series, and Etage E, at the base of the Upper Silurian series. Palse- 

 ontologically the two groups present little diflPerence so far as the 

 Graptolites alone are concerned; and I may therefore treat them 

 from the present point of view as being inseparable, or rather T may 

 confine my remarks altogether to Etage E. The following Table 

 shows the number of species common to Etage E and the mudstones 

 of the Coniston series. 



Boliemian Graptolites derived from Britain. 



Climaeograpsus teretiuscukis, His. ^ 

 Diplograpsus folium, His. 



palmeus, His. 



Graptolites bohemicus, Barr. 



colonus, Barr, 



priodon, Barr Species in Barrande's Etage E de- 



lobifenis,_ilfcCoy ^^ ^.j^^^ ^^^^ ^j^^ Coniston Mud- 



stones of the north of Englajid. 



Sedgwickii, Portl. 

 ■ — — ■ Sagittarius, His. 



Nilssoni, Barr. 



• turriculatus, Barr. 



Eastrites Linnrei, Barr. 



peregrinus, Barr. 



Ketiolites Geinitzianus, Barr. ^ 



From this Table it will be seen that no less than fourteen species 

 of Graptolites known in Etage E, at the base of the Upper Silurian 

 series of Bohemia, are identical with species which lived in the older 

 area of the Coniston Mudstones of the north of England. There 

 need therefore be little hesitation in accepting Barrande's view that 

 the Graptolites of the Bohemian area were derived by migration from 

 the British area. Many of the species are common to the Lower 

 Llandeilos of the south of Scotland; but that the migration was from 

 the Coniston rather than the Scotch area is shown by the total absence 

 in Bohemia of the genus Didymograjpsus. The Bohemian area, there- 

 fore, must have been stocked by a migration which took place at the 

 end of the Caradoc period, rather than towards its commencement, 

 the Saxon area being chiefly peopled at the latter epoch. 



The close and numerous points of resemblance between the Grap- 

 tolites of Barrande's Etage E and the mudstones of the Coniston 

 series, formerly led me to think that Etage E should be removed to 

 the summit of the Lower Silurian series (Quart. Journ. Geol. Soc. 

 vol. xxiv.). This opinion, however, was formed hastily, and without 

 a due consideration of the facts bearing upon the distribution of the 

 Graptolites ; and I must now fully admit that M. Barrande's expla- 

 nation of the facts is a more satisfactory solution of the difficult}^, 

 whilst it harmonizes entirely with the other facts which I have put 

 together on this subject. It appears, then, that the diprionidian 

 genera Climaeograpsus and Diplograpsus are not, as formerly though tj 

 exclusively confined to the Lower Silurian series, but that in 

 Bohemia, at any rate, they extend their range into the Upper Silu- 

 rians. These two genera, however, have not been shown to trans- ; 

 cend in other localities the limits of the Lower Sihman series ; whilst 



