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 Diplograpsus 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. bifidus, Hall, D. 
V-fractus, Salt., D. affinis, Nich. (MS.), D. patulus, Hall, D. 
geminus, His., D. serratulus, Hall, and D. sextans, Hall. Of 
these the first four are exclusively confined to this horizon in 
the stratified series; D. geminus, His., and D. patulus, Hall, 
are also very characteristic fossils im 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. flaccidus, Hall, D. divaricatus, Hall, 
D. sextans, Hall, and D. anceps, Nich., of which D. Murchi- 
soni, though curiously local in its occurrence, is perhaps one 
of the most characteristic. It is worthy of remark that no 
Didymograpsus 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. flaccidus. In 
Treland, however, at least two species of Didymograpsus are 
said to occur in strata of Caradoc age (Baily). 
The genus Rastrites 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, 2. peregrinus, Barr., R. Lin- 
ner, Barr., and 2. capillaris, Carr., are characteristic fossils ; 
and the two former of these are also found in the Coniston 
Flags. 
The genus Pleurograpsus, 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. 
Helicograpsus, Nich., comprising the single species 1. gra- 
ctlis, Hall (the Graptolithus gracilis of Hall), is found in the 
