LIFE IN THE EARLY CAMBRIAN 25 



borrowed from Beecher,^ shows the limbs of a 

 species, not of the Lower Cambrian, but of a some- 

 what later formation. There can be no doubt, how- 

 ever, that those of earlier species were equally per- 

 fect, more especially as Triarthrus is an animal of an 

 old type approaching to extinction in the age suc- 

 ceeding the Cambrian, and its representatives in the 

 earlier and palmy days of the family could not 

 have been inferior in organization. These creatures 

 swarmed in every sea in the Cambrian period, 

 and were represented by a great number of spe- 

 cies, some of them of large size, others very small ; 

 some many - jointed, others few - jointed, and with 

 a great variety of tubercles, spines, and other orna- 

 mental and protective parts. If we ask for their 

 affinities and place in the great group of Crustacea, 

 the answer must be that, while in some points allied 

 to the higher forms, they approach most nearly to 

 those which occupy a medium position in the class, 

 and are, in fact, a composite type, presenting points 

 of structure now distributed among different groups. 

 If we ask for affinities with lower groups, we have 

 to reply that their nearest allies in this direction are 



* America?! Journal of Science^ 1896. 



