TRILOBITA—OPISTHOPARIA. 307 



A. Glabella with one pair of lateral lobes T. 



I. Median lobe conical LIII. Conolichas. 



I. Median lobe not conical i. 



I. Median lobe subquadrate Lll. Atnphilichas. 



1. Median lobe constricted in the middle LI. Arctinurus. 



B. Glabella with two pairs of lateral lobes IT. 



II. Occipital lobes situated posteromedially from the posterior pair of laterals. 



LVI. Metopolichas. 

 11. Occipital lobes situated posterolaterally of posterior pair of laterals 2. 



2. First lateral furrow extending backward to the neck furrow. 



LV. Dicranopeltis. 

 2. First lateral furrow extending backward to the posterolateral lobe. 



LIV. Corydocephalus . 



LI. Arctinurus Castelnau. 

 Median lobe of glabella constricted in the middle and extending 

 to neck furrow; only an anterior pair of lateral lobes (the union 

 of the first and second laterals) present, and extending to the neck 

 furrow; occipital lobes absent. Pygidium with axis of one or two 

 segments reaching about half way to posterior border, the broad 

 post-axial region with a notched margin ; side lobes with three 

 pairs of grooved segments, the two anterior at least ending in free 

 points. Siluric. 



Fig. i6i8. Lichas [Arciinurus) boltoni, 

 much reduced. (After Hall. ) 



m 



Fig. 1 6 19. Amphilichas min- 

 ganensis, cephalon nearly complete 

 and pygidium, X f- (After Ray- 

 mond. ) 



135. A. boltoni (Bigsby). (Fig. 1618.) Siluric. 



Glabella with an anterior nasute extension. Eyes usually 

 crushed, looking in form and position like a second pair of lateral 

 lobes. Pygidium wider than long, deeply notched. 



