Trilobita . 
79 
up the body or roll it up in a sphere, like wood-lice (as shown by Table-c 
two of the specimens of Calymene blumenbachii in Table-case 17) ; No - 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 Palaeozoic period, at the close of which the group 
became extinct. 
A restoration and drawings of Triarthrus becki and a few 
specimens and casts of other Trilobites are exhibited in Table-case 
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). 
