LIFE IN THE EARLY CAMBRIAN 



39 



If now in imagination we cast our tow-net or 

 dredge into the sea of the Lower Cambrian, we 

 may hope to take specimens illustrative of all our 

 six groups of invertebrate animals, and under 

 several of them examples of more than one subor- 

 dinate group. Of the Crustaceans we might have 

 representatives of four or five ordinal groups, and 



Fig, 8. — Diag?-arnmatic section of two Lamina of Cryptozoon, show- 

 ing the Canals of the intermediate space, or Strojna {magnified). 

 Specimen in Peter Redpath Museum. 



of the Mollusca as many. These are the two 

 highest and most complicated. In the four lower 

 groups we would naturally have less variety, though 

 it would seem strange, were it not for so many 

 examples in later periods, that the dominant and 

 highest groups should be most developed in regard 

 to the number of their modifications. 



Of the whole we might perhaps have been able 

 to secure at least 200 species even in one locality. 



