TRILOBITES AND OTHER FOSSIL CRUSTACEA. 191 



In the Carboniferous Trilobites (Phillipsia, etc.) the 

 carapace seems to have contained more limy matter 

 in its composition than other species. In this genus 

 we always find the moultings in the two parts of body 

 and tail, and head. In the Calymene (Fig. 140) the 

 thoracic or ringed part is frequently found by itself, 



Fig. 156. Head shield and 

 Caudal shield QiPhillipsia. 



Fig- **>$. PJiacops caudatus. Fig. 157. Trinuclens LloydtL 



and not seldom the rings are detached, as if the whole 

 mechanism of the coat-of-mail-like armour had be- 

 come loosened and got scattered about. Undoubtedly 

 the chemical composition of the carapace differed 

 accordingly as the habits of the Trilobites varied. 



