EXPLANATION OF PLATES. 205 



PLATE X. 



DiKELOCEPHALUS SPINIGER. 



Fig. 1. Glabella and part of the fixed cheeks, showing the base of a spine on tho 

 occi])ital ring. 

 «♦ 2. An imperfect pygidium, associated in the same stone with the head. 



DiKELOCEPHALUS, Sp.? 

 «« 3. The cheek of a species which has not been identified : from Lake Pepin. 



DiKELOCEPHALUS MISA. 

 Fig. 4. The glabella and part of the fixed cheek. 

 «* 5. A pygidium occurring in the same association; and the same is found on the 



specimens with fig. 4. 

 «« 6. A part of a thoracic segment of this species? from the same block on which 



the glabella occurs. 

 «• ?7 Sc 8. Imperfect movable cheeks, apparently belonging to D. misa; occurring 

 in beds where no other species of the genus are known. 



DiKELOCEPHALUS MINNESOTENSIS, vav. 



Fig 9. The glabella and fixed cheeks, having the frontal limb slightly extended in 

 the centre : Stillwater. 



DiKELOCEPHALUS MINNESOTENSIS. 

 Fig. 10. A head, restored from actual specimens of the glabella and cheeks. 

 «« 11. Part of a thoracic segment which has apparently been a little bent near the 



axis. 

 «• 12. A thoracic segment, more than half of which, on the left side, is from an 

 actual specimen : the other part is restored to correspond with it. 



DiKELOCEPHALUS PEPINENSIS. 

 Fig. 13. The central portion of a small head. 

 «' 14. A restored figure of a head from actual specimens. 



** 15 8c 16. Thoracic segments from different parts of the body, showing a little 

 difference in the direction of the furrow. These segments occur in specimens 

 associated with the heads, cheeks and pygidia of this species. 



** 17- A pygidium of the same species. 



DiKELOCEPHALUS OSCEOLA. 

 Fig. 18. The head, twice enlarged. 

 <« 19. A cheek, natural size : found in the same stone. 



Chariocephalus whitfieldi. 

 Fig. 20. A head restored from actual specimens of the glabella and cheeks. 



Ptychaspis miniscaensis. /i"^: 



Fig. 21. A head restored from actual specimens of the separate glabella and movable 

 cheeks. The cheeks appear narrower than when given separately ; as they 

 are shown in perspective, to correspond with the convexity of the head. 



«♦ 22. A thoracic segment : the righthand extremity is restored, to correspond with 

 the actual portion on the left. 



Agnostus parilis. 

 Fig. 23. A head, three times enlarged. 

 «• 24. A pygidium, enlarged in equal degree. • 



Agnostus disparilis. 



Fio. 25. A head, four times enlarged. 

 «« 26. The pygidium? of this species, four times enlarged. 

 «< 27. A pygidium showing transverse furrows, equally enlarged. 



