728 



ARTHROPODA 



THYLUM VII 



northern parts of Europe, and those of the middle and southern portions. While the 

 majority of northern genera and sjiecies are common to Great Britain, Scandinavia 

 and Russia, the forms of the central European provinces (Bohemia, Thuringia, Fichtel- 

 berg, the Hartz, Belgium, Brittany, Northern Spain, Portugal, the Pyrenees, the Alps 

 and Sardinia) are so dissimilar as to stand in closer relationships with the North 

 American than with the first-named Trilobite fauna. Of the 350 species found in 

 Norway and Sweden, and of the 275 species in Bohemia, only six are common to 

 both provinces, and it is doubtful if these are really identical. 



The first of the accompanying taljles shows the range and relative development of 

 the orders and the subclass ; the second represents the vertical range of the several 

 families of Trilobites. 



TABLE I 



Diagram Constructed by Beecher showing Relative Development 



OF THE Orders of Trilobites 



Permian. 



Carboniferous. 



Devonian. 



Silurian. 



Ordovician. 



Cambrian. 



Pre-Cambrian. 



[Table 



