Fink : LICHENS OF THE MINNESOTA VALLEY. 289 



Placodium vitellinum (EiiRH.) NAEG. and HEPP., CTS. 

 Lecanora rubina (VILL.) ACH., CTS. 



Lecanora rubina (VILL.) ACH. var. heteromorpha ACH., CS. 

 Lecanora subfusca (L.) ACH., S. 

 Lecanora varia (EHRH.) NYL.. AS. 

 Lecanora cinerea (L.) SOMMERF., CTS. 

 Lecanora xanthophana NYL., C. 

 Rinodina oreina (Acn.) MASS., C. 

 Rinodina sophodes (Acn.) NYL. 

 Biatora rufonigra TUCK., T. 

 Biatora myriocarpoides (NYL.) TUCK., A. 

 Buellia spuria (SCHAER.) ARN., CT. 

 Buellia petraea (FLOT., KOERB.) TUCK., CTS. 

 Endocarpon miniatum (L.) SCHAER. var. complication 

 SCHAER., C. 



Comparing the above lichen formation with the similar ones 

 at Pipestone and Granite Falls we find it to contain only two 

 species which are additions to the three at the two places just 

 named. These I have marked (A). It is about as extensive 

 an area as the two at Pipestone combined, has about the same 

 number of lichens as both and has 12 species (marked C) which 

 are common to all the exposed rock lichen formations in the 

 area considered in this paper. In general these 12 species may 

 be regarded as the most constant of the exposed Archean and 

 Algonkian rock lichen formations of southwestern Minnesota. 

 As we. multiply areas of comparison and especially as we introduce 

 those at a greater distance the number of common floral elements 

 very naturally decreases. Thus considering the similar forma- 

 tion at Taylors Falls, we find only 8 species (marked T) com- 

 mon to it and all the similar ones previously considered, and 

 passing to the corresponding formation at Gunflint in the lake 

 Superior region, the number found in all these similar forma- 

 tions in widely separated areas of the state is found to be only 

 6 (marked S). These 6 species may be looked for with con- 

 siderable certainty wherever such lichen formations are well de- 

 veloped in the state. Other elements will vary according to 

 relation to other adjacent formations, position northward or 

 southward and in some instances eastward or westward in 

 the state and to various ecologic factors which cannot be enum- 

 erated fully. 



