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Explanation of the Plates. 



PLATE V. 



DlKELOCEPHALUS SPINIGER. 

 Fig. 1. Glabella and part of the fixed cheeks, showing the base of spine on the occipital ring. 

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



DlKELOCEPHALUS, Sp. ? 

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



DlKELOCEPHALUS 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 fi- 4. 



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

 occurs. 



" ? 7 & 8. Imperfect movable cheeks, apparently belonging to B. misa / occurring in beds 

 where no other species of the genus are known. 



DlKELOCEPHALUS MINNESOTENSIS, VGLT. 

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

 Stillwater. 



DlKELOCEPHALUS 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 speci- 

 men : the other part is restored to correspond with it. 



DlKELOCEPHALUS PEPINENSIS. 

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

 " 14. A restored figure of a head from actual specimens. 



" 15 & 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. 



DlKELOCEPHALUS OSCEOLA. 

 Fig. 18. The head twice enlarged. 

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



ClIARIOCEPHALUS WHITFIELDI. 

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



Ptychaspis miniscaensis. 



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 right hand 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. 



Fig. 25. A head, four times enlarged. 

 " 26. The pygidium of this species ? four times enlarged. 

 " 27. A pygidium showing transverse furrows, equally enlarged. 



