102 HISTORICAL PALAZONTOLOGY. 
rent than real in Bohemia, they are exclusively confined to 
strata of Lower Silurian age, and are not known to occur in 
Fig. 40.—Central portion of the colony of Didymograptus divaricatus, Upper 
Llandeilo, Dumfriesshire. (Original.) 
the Upper Silurian. Lastly, there is a group of Graptolites 
(Phyllograptus, fig. 42) in which the colony is leaf-like in form, 
TA 
=F 
q 
wry rips 6 
Fig. 41.—Examples of Diplograptus 
pristis, showing variations in the appen- 
dages at the base. 
Fig. 42.—Group of individuals of Phyddo- 
Dumfriesshire. 
graptus typus, from the Quebec group of 
Upper Llandeilo, Canada. (After Hall.) One of the four rows 
(Original.) of cells is hidden on the under surface. 
and is composed of fowr rows of cells springing in a cross-like 
