of the British Species and Genera of Graptolites. 351 



only British species as yet known to be confined to the Coniston 

 Flags. 



The genus Dicranograpsus^ Hall, comprising the single 

 species D. ramosus (the old Dijylograjpsus ramosus)^ ranges 

 through the Lower and Upper Llandeilos, and is said to have 

 been found in the Coniston Flags (Caradoc) . It is, however, 

 most characteristically a fossil of the Upper Llandeilo rocks 

 in Britain. 



The genus Didymograpsus appears to have both its com- 

 mencement and its maximum in the Skiddaw and Quebec 

 groups, being represented in Britain by eight species from the 

 Skiddaw Slates, viz. D. nitidus^ Hall, D, hifldusj Hall, D. 

 V-fractuSj Salt., D. affinis^ Nich. (MS.), D. patulus^ Hall, D. 

 geminuSj His., D. serratulus, Hall, and I), sextans j Hall. Of 

 these the first four are exclusively confined to this horizon in 

 the stratified series; D. geminus, His., and D. jpatulus^ Hall, 

 are also very characteristic fossils in the Lower Llandeilo 

 rocks ; D. sextans^ Hall, occurs plentifully in the Upper 

 Llandeilos, and D. serratulus is found in the Utica Slate (Ca- 

 radoc) of America. In the Upper Llandeilo rocks the genus 

 Didymograpsus is highly characteristic, and is represented by 

 D. Murchisoni^ Beck, D. jlaccidus^ Hall, D. divaricatus^ Hall, 

 D. sextans J Hall, and D. anceps^ Nich., of which D. Murchi- 

 sonij though curiously local in its occurrence, is perhaps one 

 of the most characteristic. It is worthy of remark that no 

 Didynfiograpsns has hitherto been found in the Caradoc group in 

 England, not even in the Coniston Flags, though these abound 

 in Graptolites and contain so many species common to the 

 Utica Slates of America, in which the genus is represented by 

 D. sextans^ D. serratulus^ D. divaricatus^ and D.faccidus. In 

 Ireland, however, at least two species oi Didymograpsus are 

 said to occur in strata of Caradoc age (Baily). 



The genus Ro^trites of Barrande appears not to occur either 

 in the Skiddaw Slates or in the Lower Llandeilo proper, but 

 to be exclusively confined to the Upper Llandeilo and Caradoc 

 groups. In the former of these, R. peregrinus^ Barr., R. Lin- 

 nceij Barr., and R. capillarisj Carr., are characteristic fossils ; 

 and the two former of these are also found in the Coniston 

 Flags. 



The genus PleurograpsuSj Nich., is doubtfully represented 

 in the Skiddaw Slates by a single species, P. vagans, Nich., 

 the typical form (viz. P. linearis^ Carr.) being confined to the 

 Upper Llandeilo rocks. 



HelicograpsuSj Nich., comprising the single species H. gra- 

 cilis ^ Hall (the Graptolithus gracilis of Hall), is found in the 



