14 THE DETEKMIXATTON OF IJCnE>S IN THE FIELD 



2o. A p. ipruinose Lecanora (Pallida group, 27-32). 



Ap. not pruinose Lecanora (Subf usca group, 11-19). 



26. Th. normallj svibeffigurate at the margin. 



^ ^ On rocks Lecanora (Galactina group, 33-35). 



Th. not subeffigurate at the margin. On 



rocks, etc Lecanora (Umbrina group, 21-2o) 



27. Sp. ellipsoid, 1-3-septate, usu. less than 20 /x 



long and about three times as long as broad. Lecania (i). 

 Sp. fusiform, 1-3-septate, 13-27 X 4-6 ya, 



and usu. about 4 times as long as broad ... Icmadophila. 

 Sp. acicular, 3-7-septate, usu. over 40 /x long 



and about 10 times as long as broad \ Hsematomona. 



28. Algal cells Trentepohlia. Sp. colourless, 



fusiform, many-septate and slightly muri- 



f orm. On trees \ Thelotrema. 



Algal cells green. Sp. and habitat various... 29. 



29. Sp. colourless, elongate cylindrical, 30-40 



septate, about 100 x 4 //. On trees Conotrema. 



Sp. colourless or dai-k, distinctly muriform, 



ellipsoid. Habitat various . . ." 30. 



30. Sp. colourless, often large (over 50 yu long). 



^ On trees ."... Phlyctis. 



Sp. dark, usu. less than 40 ^ long. On I'oeks, 



lichens, or mosses Diploschistes. 



31. Th. thin, having a varnished appearance or 



wanting. Podetia very short. Sp. fili- 

 form, man3'-septate, 180 X 2 ^/ Gomphillus. 



Th. granular. Sp. simple or with few septa, 



never filiform 32. 



32. Podetia solid or nearly so. Sp. colourless, 



simple or septate 34. 



Podetia distinctlj^ hollow. Sp. colourless, 



simple 33. 



33. Pjdetia very short, papilla-like, ^club- 



shaped, inflated Pycnothelia. 



P )detia usu. well-developed, sometimes cup- 

 shaped at apex Cladonia. 



34. Podetia granular or minutely squamulose ... 35. 

 Podetia without granules or squamules. 



Thalline squamules K-f yellow. Usu. on 



earth BsBomyces. 



35. Podetia finely Avarted, simple (unbranched). 



A]), black Pilophorus. 



Podetia minutely squamulose, often ± branched. 

 Ap. brown Stereocaulon. 



(«) It is often impossible to determine crustaceous lichens in the 

 field, but this and the following keys have been arranged with their 

 use in the field kept constantly in view. 



{h) Occasionally the myxophycean alga appears to be reddish or 

 3xllowish. 



