102 



HISTORICAL PALEONTOLOGY. 



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 Didyttirgraptiis 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, 



m 



Fig. 41. Example 

 pristis, showing variations in the appen- 

 dages at the base. Upper Llandeilo, 

 Dumfriesshire. (Original.) 



Fig. 42. Group of individuals of Phyllo- 

 graphts typns, from the Quebec group of 

 Canada. (After Hall.) One of the four rows 

 of cells is hidden on the under surface. 



and is composed of fjur rows of cells springing in a cross-like 



