DESCRIPTION OF THE PLATES. 



PLATE I. 



Eigs. 1 to 23. Comparative size of spores. 



1. Pertusaria communis. 



2. Opegrapka siderella. 



3. Thelotrema lepadinum. 



4. Aulacographa elegans. 



5. Peltigera horizontalis. 



6. Bticta scrobiculata. 



7. Lecanora pallescens, var. 



parella. 



8. G? , aphis scripta. 



9. Urceolaria scruposa. 



10. Stereocaulon paschale. 



11. Solorina crocea. 



12. Physcia ciliaris. 



13. Verrucaria nitida. 



14. Lecidea geograpMca. 



15. Z. aeruginosa. 



16. Ramalina fraxinea. 



1 7 . Umbilicaria polymorplia. 



18. Lecidea ferruginea. 



19. Lecanora subfusca. 

 2 0 . Parmelia parietina . 



21. Efona barbata. 



22. Calicium hyper ellum. 

 2 3 . Cladonia pyxida ta . 



* The majority of the Illustrations are original. For the drawings of the 

 spermogones and spermatia, pycnides and stylospores, and a few others, we 

 are indebted to the Memoir of Tulasne. Several drawings illustrative of ge- 

 neral characters or structure have been taken from the works of Leighton and 



