PLATE XXII. _ 



IlL^NUS AR3IATUS, HaLL. 

 Pages 418, 433. 



Fig. 1. Upper view of the head of a well preserved individual. 

 " 2. Profile view of the same. 



" 3. The pygidium and last thoracic segment, found associated with the head and supposed to 

 be of the same species. 



Ill^nus [Bumastus) ioxus, Hall. 



Page 420. 



Fig. 4. Upper view of the head of a small individual. 



" 5. Profile view of the same. 



" 6. Upper view of a medium sized individual. 



" 7. Lower view of the same, showing the extent of the infolding of the border, and the direc- 

 tion of the suture on the under surface. 



" 8. Profile view of the same individual. 



" 9. The movable cheek of a large specimen. 



" 10. A pygidium of the form commonly found associated with the other remains referred to 

 this species. 



" 11. A small glabella, referred with doubt to this species. ' 



Ill^^nus cuniculus. Hall. 



Page 421. 

 Fig. 12. View of the glabella of this species. 



Ill^nds INS16NIS, Hall. 



I Page 419. 



Fig. 13. The glabella and fixed cheeks, with the movable cheeks restored in outline, 

 " 14. The pygidium referred to this species. 



Illmnus imperator, Hall. 



Page 420. 



Fig. 15. The head of a large individual. The figure is reduced to one-half the natural size. 

 " 16. The pygidium of a very small specimen of the species. 

 " 17. The pygidium and parts of four of the thoracic segments, reduced in size one-half. 



