viii ILLUSTRATIONS. 



Pane. 



Plate XL. Rhizostomites admirandus 184 



XLI. Rhizostomites lithographicus 186 



XI. II. Rhizostomites lithographicus ; R. admirandus; Medusina staurophora 188 



XLI 1 1. Hexarhizites insignia 190 



XLIV. Medusina deperdita; Acraspedites antiquus; Medusina porpitina 192 



XLV. Medusina quadrata; M. bicincta; Eulithota fasciculata 194 



XLVI. Medusichnites 196 



XLVII. Discophyllum pel tat urn 198 



Fig. 1. Brooksella alternata; diagrammatic central vertical section 9 



2. Archirhiza primordial is; snbumbrella view 10 



3. Canuoi hiza connexa; ail radial section 11 



4. Brooksella alternata ; diagrammatic central vertical section through the umbrella lobes 



(siime as fig. 1; 28 



5. Brooksella alternata; diagrammatic central vertical section through the central axis 



between the radiating lobes 29 



6. Brooksella alternata; diagrammatic vertical section through the central axis of fig. 



4b of PI. I 29 



7. Brooksella alternata: diagrammatic vertical median section of same specimen as fig. 6. 29 



8. Laotira cambria; diagrammatic vertical section of the specimen represented by fig. la 



of PI. XVIII 34 



9. Laotira cambria; transverse section of a complex specimen 34 



10. Laotira cambria; diagrammatic transverse section of a complex form 35 



11. Laotira cambria; hypothetical canal system of the exumbrella of fig. 1 of PI. XIV 36 



12. Laotira cambria; restoration of the canal system of the snbumbrella lobes of the 



specimen illustrated by fig. 1 of PI. XII 37 



13. Laotira cambria; theoretical diagram of the canal system of the exumbrella and sub- 



umbrella lobes of fig. 2 of PI. XII 37 



14. Bythotrephis ( }) asteroides 42 



15. Dactyloiditea asteroides from Parker's quarry, Georgia, Vermont 40 



16. Medusina radiata 58 



17. Senueost oinites zitteli _ 71 



18. Rhizostomites 80 



19. Rhizostomites 81 



20. Hexarhizites insignis 87 



21. Leptobrachites trigonobrachins 89 



22. Leptobrachites trigonobrachins - 90 



23. Medusina deperdita 92 



24. Medusina atava 96 



25. Medusites ( !) latilobatus 99 



2ii. Enlarged section of a portion of Medusites l ?) latilobatus 100 



