374 



ARTHROPODA. 



body -rings, and the tail is sub -triangular. Endymion is 

 allied to both Trinudeus and Ampyx, but wants the perforated 

 border of the former, and the prolonged glabella and genal 

 spines of the latter. 



12. ASAPHIM. Large Trilobites, generally oval, and never 

 furnished with spines or tubercles on their surface. The 

 eyes smooth, and the facial sutures terminating 011 the pos- 

 terior margin. The cephalic and caudal shields generally of 

 large size, the glabella of the former often obscure, and the 

 latter sometimes exhibiting no indication of its component 

 segments. The body-rings usually eight in number, with 

 grooved pleurse. The family is characteristically Lower 

 Silurian, and the two principal genera are Asaplius and 

 Ogygia. In the genus Asaplius (figs. 211, 215, 232) the 

 general trilobation is somewhat indistinct, and the caudal 



Fig. 232. Asaphus tyrannus. Lower 

 Silurian. (After Salter.) 



Fig. 233. Ogygia Buchii. Lower 

 Silurian. (After Salter.) 



shield is at least equal to the head in size. The genal 

 angles of the head-shield may be rounded or spinose, and 

 the glabella is not marked off by conspicuous axal furrows. 

 The facial sutures are discontinuous, the eyes crescentic, the 

 hypostome deeply forked, and the pygidium may or may not 

 show a conspicuous axis, its hinder extremity being usually 



