SILURIAN ANIMALS. 



321 



ly, into three lobes (hence the name) — a middle, a right, and a left. 

 The viscera were contained in the middle lobe, the two side lobes 

 being extensions of the shell, as seen in the section, Fig. 375, b. Well- 



Fig. 371. 



Fig. 372. 



Figs. 371, 372.— Silurian Annelids : 371. Conmlites serpentarius (Worm-Tube). 



an Annelid (after Hall). 



?2. Trail of 



organized compound eyes are distinctly seen in well-preserved speci- 

 mens on the lateral lobes of the head-shields (cheeks) (Fig. 374). The 

 under side of the animal has never been distinctly seen, and therefore the 



*tX5 <6x5 exio 



Fig. 373.— Worm-teeth from Cincinnati group, enlarged (after Hinde). 



character of the locomotive organs is not certainly known. But until 

 recently it was believed that, like some of the lower crustaceans of the 



Fig. 374.— Structure of the Eye of Trilobites: a, Dalmania pleuropteryx ; b, eye slightly magnified: 

 c, eye more highly magnified; d, small portion still more highly magnified (after Hall). 

 21 



