N PLATE XXVII. 



PAGE. 



Pig. 1. Acidaspis OrToni Poerste .522 



1. A head. B. O. 



Fig. 2. Proetus determinate Foerste 523 



2. A glabella with part of anterior border ; same as figure 5 of plate XXVI. S. H. O. 

 Fig. 3. PrcETus determinaTus Foerste , 523 



3. A' glabella, S. H. O. 



Fig. 4. Phacops trisui,caTus Hall , 529 



4. Probably a pygidum of this species S. H. O. 



Fig. 5. Cyphaspis Clintonensis Foerste 524 



5. Glabella. B. O. 



Fig. 6. Itj^nus dayTONEnSiS Hall and Whitfield 525 



6. A rostrum in position. B. O. Collection of Prof, W. S. Hoskinson. 



Fig. 7. Ili^nus madisonianus Whitfield 526 



7. Glabella. B. O. 



Fig. 8. Iia^Enus madisonianus Whitfield 526 



8. Pygidium ; moderately elongated. B. O 



Fig. 9. Iix^nus madisonianus Whitfield 526 



9. Pygidium, very slightly elongated. B O. 



Fig. 10. Ili^Enus madisonianus Whitfield •. 526 



10. Pygidium not at all elongated, all these specimens are only very small forms of 



the species. 



Fig. 10a. Ili^nus daytonensis Hall and Whitfield 525 



10a. Movable cheek, Ludlow Falls, O. 

 Fig. 11. I/ICHAS 



11. Hypostoma, differing considerably from that of L breviceps, and possibly belong- 



ing to a poorly preserved apparently distinct form, described in the text as 

 ° Lichas phlyc ainoides 

 Fig. 12. Calymene vogdesi Foerste 526 



12. Head, same as figure 25 of plate XXV C. O. 



Fig. 13. CalymenE VOGDESI Foerste 526 



13. Outline of the preceding head. CO. 



Fig. 14. CalymenE vogdesi Foerste 526 



14. Part of head, same as figure 24 of plate XXV, reconstructed from fragments. 



S. II. O. In the middle limei-tones 

 Fig. 15. Cai/ymene vogdesi Foerste o26 



15. Outline of the preceding head. S. H. O. 



Fig. 16. Cai/vmene vogdesi Foerste 526 



16. A characteristic pygidium, associated with forms like those shown in figure 12 



and 18. C. O. 



Fig. 17. Ceraurus (pseudosph^rexochus) ci/intonensis Foerste 527 



17. A Glabella. B. O. 



Fig. 18. Lichas breviceps Hall 529 



18. Of the form with a veiy distinct lobe towards either end of the occipital furrow, 



a characteristic of the Clinton specimens, hence called variety Clintonensis. 

 B O. 



Fig. 19. Lichas breviceps Hall 529 



19. Hypostoma. B. O. 



Fig. 29. Phacops Trisulcatus Hall 529 



20. Part of head, same as figure 8 plate XXVI, B. O. 



Fig. 21. Phacops Trisuixatus Hall..: 529 



21. Head, a more perfect specimen. S. H. O. 



