102 



HISTORICAL PALAEONTOLOGY. 



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 Did) wcgraptus divaria 

 Llandeilo, Dumfriesshire. (Original.) 



the Upper Silurian. Lastly, there is a group of Graptolites 

 $-, fig. 42) in which the colony is leaf-like in form, 



Fig. 41. Examples of Diplograptus 

 pristis, showing variations in the appen- 

 dages at the base. Upper Llandeilo, 

 Dumfriesshire. (Original.) 



Fig. 42. Group of individuals of Phyllo- 

 graptns typus, 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 four rows of cells springing in a cross-like 



