THE TRILOBITA AND OTHER ARTHROPODA 199 



The pygidium consists of twelve or more somites, of 

 which only ten have pleura recognizable : it is longer 

 proportionately than that of Calymene, more triangular in 

 outline, its axis narrower, and at its posterior end it is 

 drawn out to a long spine (mncronate). The presence 

 of this spine shows, by analogy with living Arthropods, 

 that it obtained its food by thrusting its head forward 



FIG. 56. DALMANITES CAUDATUS (BRUNNICH), WENLOCK 



LIMESTONE. 

 (Natural size.) (After Salter.) 



F.S., Facial suture. 



into the mud, using the tail-spine as its support. The 

 highly-developed eyes, however, show that it did not 

 live buried in the mud : the eyes could have been no use 

 in the search for food ; they must have served to warn 

 it of the approach of enemies. Their position, on the 

 highest part of the hea'd, is clear evidence that this was a 

 bottom-living or^ benthic animal : in trilobites of nectic 



