of the British Species and Genera of Graptolites. 353 
either the Skiddaw Slates or the Lower Llandeilo proper, though 
its discovery in the former of these may fairly be anticipated. 
In the Upper Llandeilo rocks of the south of Scotland a single 
species has been found, apparently &. venosus, Hall; and a 
second species, &. perlatus, Nich., occurs in the Coniston 
Flags; but this may possibly turn out to be a large variety of 
the former. The third and longest-lived British species is R. 
Geinitzianus, Barrande,which occurs plentifully in the Coniston 
Flags (Caradoc), and has also been found in the Ludlow rocks 
of the Pentland Hills, near Edinburgh. 
The genus Ptilograpsus, Hall, is known as occurring in 
Britam by a single species only, P. anglicus, Nich., which is 
found in the Lower Ludlow rocks. The two remaining spe- 
cies of Ptilograpsus occur in the Quebec group in Canada; 
but no member of the genus has as yet been discovered in any 
of the intervening formations. 
Summary. 
Of the above-mentioned British genera of Graptolites, in 
number seventeen, it will be seen that fourteen are, as far as 
is yet known, entirely and exclusively confined to the Lower 
Silurian series, two are common to both the Lower and Upper 
divisions, and P#lograpsus alone is confined to the Upper 
Silurian rocks. As, however, this last-named genus is found 
in the Quebec group, the Upper-Silurian period cannot be 
said to possess a single characteristic genus of the family, and 
it possesses but two peculiar species. 
In the Tremadoc Slates (Upper Cambrian ?) no other genus 
is known to occur than Dictyonema, and this is represented by 
a single species. The Skiddaw Slates (Lowest Llandeilo) are 
specially characterized by the exclusive possession of the ge- 
nera Dichograpsus, Tetragrapsus, and Phyllograpsus, and of 
the species Diplograpsus antennarius, D. pristiniformis, Didy- 
mograpsus nitidus, D. V-fractus, and D. affinis. The Skiddaw 
Slates contain altogether eight genera and twenty-four species, 
of which three genera and thirteen species belong also to the 
(Quebec group. ‘Two species occur also as characteristic fossils 
in the Lower Llandeilo rocks of Wales and Sweden. Five 
species are peculiar to the Slates, and the remaining four 
occur either in the Upper Llandeilo or in the Caradoc groups. 
Out of nineteen species, not peculiar to the Skiddaw Slates, 
thirteen, or more than two-thirds, are common to the Quebec 
group of Canada, a close relationship between the two forma- 
tions being thus demonstrated. 
The Lower Llandeilo rocks proper are specially charac- 
Ann. & Mag. N. Hist. Ser. 4. Vol. ii. 2 
