3o6 NORTH AMERICAN INDEX FOSSILS. 



L. Bronteus Goldfuss. 



Cephalon less than one third the entire length. Genal angles 

 pointed. Glabella rapidly expanding anteriorly; glabellar furrows 

 indistinct or obsolete. Free cheeks larger than the fixed. Eyes 

 near the posterior border. Thorax of ten segments. Pygidium 

 longer than cephalon or thorax; axis very short, with radiating 

 furrows extending fan-like from it toward the margin. Ordovicic- 

 Devonic. 



133. B. lunatus Billings. (Fig. 1617.) Ordovicic. 

 Pygidium marked by six ribs radiating from each side of the 



axis ; the posterior ones are straight, the anterior curved backwards. 

 The axial rib is at times slightly bifid ; all ribs flatten out and dis- 

 appear as they approach the margin. 



Trenton of New Jersey, Minnesota and Quebec. 



134. B. acamas Hall. Siluric. 

 Dorsal furrows extending slightly more than one third the entire 



length of the head from the neck furrow; posterior pair of gla- 

 bellar furrows cutting off a pair of basal lobes ; a pair of occipital 

 lobes present. Pygidium with seven slightly elevated ribs radiating 

 from each side of the short axis, each curving first backward and 

 then outward; axial rib with twice the width of the others at the 

 end of the axis and with sides curving outward more and more 

 rapidly until it ends in a width of four or five times that at its 

 beginning. All ribs fade out before reaching the margin. 

 Niagaran of Illinois and Wisconsin. 



LI-LVI. LiCHADiD^E Barrande. 



Cephalon not more than one fourth the entire length; genal 

 angles spiniform. Glabella broad, with very prominent central 

 lobe and one to three lateral lobes on each side. Eyes small. 

 Thorax with nine to eleven segments and with grooved and sickle- 

 shaped pleura. Pygidium large, flat, commonly with notched mar- 

 gin corresponding to the pleural grooves. Surface granulose. 

 Ordovicic-Devonic. 



The closely related members of the Lichas family may be sub- 

 divided as follows: 



