26 Mr. C. Lapworth on the Geological 



species apparently surviving into the Wenlock beds. Its 

 forms appear first in the Middle Birkhill beds, and crowd the 

 Upper Birkhill and Gala beds wherever they are Grapto- 

 litiferous. In the Upper Gala beds they are as yet un- 

 known. 



Group vi. (Sedgwicki group) corresponds generally with 

 the foregoing in its vertical range. None of its species is 

 known in the Lowest Birkhill ; and only a single form lingers 

 on into the Upper Gala period. The supposed Wenlock 

 examples of this group occasionally quoted by palaeontologists 

 are probably fragmentary examples of the genus Cyrtograptus, 

 Carr. 



Of species of Monograptus worthy of notice in this place 

 M. priodon, Bronn, is perhaps the most remarkable. If the 

 Swedish palaeontologists are correct in their reference of M. 

 Flemingii, Salt., and M. ludensis, Murch., to this species, it 

 is unequalled in its range, having existed from the close of 

 the Birkhill period to the Middle of the Ludlow. 



Monograptus tenuis, Portlock, and M. gregarius, Lapw., 

 are the characteristic species of the Llandovery formation. 

 M. lobiferus, M'Coy, distinguishes the upper half of the Llan- 

 dovery formation ; and M. exiguus, Nich., is peculiar to the 

 lower division of the Tarannon. To this latter subformation 

 also the remarkable species M. turriculatus, Barr., is generally 

 restricted. M. testis, Barr., is apparently confined to a single 

 zone in the Wenlock formation ; and M. Nilssoni, Barr., and 

 M. scayiicus, Tullb., are strictly peculiar to the Lower Ludlow, 

 not only in Britain, but also upon the continent of Europe. 



Cyrtograptus, Carr. — Until very recently little was known 

 of this very elegant and peculiar genus. Generally speaking, 

 it is a very rare fossil in Britain, except along certain special 

 horizons. Our oldest forms occur in the Upper Gala beds, where 

 examples are few. In the Lower Wenlock they become more 

 common, especially in the basal zones of Cyrtograptus Murchi- 

 soni, Carr., and C. Linnarssoni, Lapw. A single species has 

 been recognized in the Lower Ludlow formation. In the 

 Gala and Wenlock formations of Scania Dr. Tullberg has 

 recently detected many new species belonging to this genus, 

 which is there, as in Britain, peculiar to the strata above 

 the Lower Gala. It is tolerably certain that similar forms 

 await discovery in the corresponding rocks of Britain, and 

 that this genus will eventually be found to characterize 

 the strata above the middle line of the Gala group, as the 

 genus Rastrites distinguishes those below it. 



The most remarkable species hitherto detected in Britain is 

 Cyrtograptus Murchisoni, Carr., which, as we have already 



