Trilohita. 79 



lip the body or roll iL up in a sphere, likt" wood-lice (as shown by Tablc-caso 

 two of the specimens of Calymcnc bluincnbacJiii in Table-case 17) ; ^°- ^''^• 

 and this habit, coupled with the strong spines with which the 

 dorsal area was frequently armed, suggests that the Trilobites 

 themselves were in need of protection from more powerful inhabi- 

 tants of the seas. 



About 2,000 species have been described from Cambrian and 

 later beds of the Palyeozoic period, at the close of which the group 

 became extinct. 



A restoration and drawings of Tiiartknis bccki and a few 

 specimens and casts of other Trilobites are exhibited in Table-ease 

 17. The attention of those who are interested in these Arthropods 

 is directed to the account of them which appears in the " Guide 

 to the Fossil Invertebrate Animals," and to the series of speci- 

 mens displayed in the Geological Department (Gallery 8, Table- 

 case 25, Wall-case 14 b). 



