Explanation of the Plates. 



335 



PLATE IV. 



DlKELOCEPHALUS PEPINENSIS. 



Fig. i. Glabella and fixed cheeks. The anterior furrows are scarcely shown in the figures. 



" 2. Pygidium of the same species. 



" 3. A cheek. 



" 4. Hypostoma of the same. 



DlKELOCEPHALUS MINNESOTENSIS. 



Pig. 5. Glabella and fixed cheeks. The frontal limb is represented in outline, from another 



specimen in which this part is preserved. From Mazomania. 



" 6. A small pygidium from Lagrange mountain. 



" 7. A large pygidium from the Magnesian limestone near Madison, Wisconsin. 



" 8. A thoracic segment ; one side restored in outline. 



" 9. Part of a small hypostoma. 



" 10. Part of a larger hypostoma. 



DlKELOCEPHALUS MINNESOTENSIS, Var. 

 Fig. 11. Glabella, fixed cheeks, and frontal limb. 



DlKELOCEPHALUS MINNESOTENSIS, var. LIMBATUS. 

 Fig. 12. A part of the glabella and frontal limb of this variety. 



Triarthrella AURORALIS. 

 Fig. 13. Glabella and fixed cheeks, twice enlarged. From Lagrange mountain. 



