LIFE IN THE EARLY CAMBRIAN 33 



more swift and powerful than themselves. But 

 what enemies of this kind had the Trilobites to 

 dread? Yet species a foot or more in length pre- 

 sented great bayonet - like spines. All that we 

 know on this subject is that on the surfaces of 

 the Lower Cambrian rocks there are in some 

 places complicated and mysterious tracks or 

 scratches, which seem to have been produced when 

 the rock was in the state of soft mud, by large 

 and swiftly swimming animals possessing some sort 

 of arms or similar appendages (Fig. 4). Matthew 

 has ingeniously suggested that they may have been 

 large Mollusks allied to the modern gigantic Squids 

 which still abound in the ocean, that they may 

 have been sufficiently powerful to prey on the 

 Trilobites, and, being swift swimmers, would have 

 found them a helpless prey but for their defensive 

 spines. Yet such large Mollusks might have 

 perished without leaving any remains recognisable 

 in the rocks, except what may be termed their hand- 

 writing on clay. A few small examples of the shell- 

 bearing species of these highest Mollusks, however, 

 appear in the Cambrian, and in the succeeding ages 

 they become very abundant and attain to large 

 dimensions, again dwindling toward modern times. 



3 



