KEY TO DERMATOLITHON 273 



4. Perithallium scantily developed; crusts superimposed and 

 individualized by the presence of a cortical cell laj^r on 

 each, but all contributing to the formation of conceptacles 5 



4. Perithallium usually of 1 to 4 layers in middle parts ; crusts 

 neither markedly superimposed nor the layers individualized 



as above 6 



5. Conceptacles 150 to 400 ju, in diameter, convex, not be- 

 coming deformed . . . D. geometricum (Lemoine) comb. nov. 



= Lithophyllum (Dermatolithonf) geometricum Lemoine 



( 1929a) Type locality: Canary Islands 

 5. Conceptacles 400 to 500 fx in diameter, convex but becoming 



deformed . . . D. prototypum (Foslie) Foshe (1909) van 



prototypum = Lithothamnion prototypum Foslie (1897) Type 



locality : West Indies 



6. Thalli 75 to 300 fi thick; perithallium cells mostly 18 to 35 

 IX. long ; tetrasporangial conceptacles 220 to 400 ju in diame- 

 ter, smaller than carposporic conceptacles . . . D. hapali- 

 dioides (Crouan et Crouan) Foslie (1900a) = Melobesia 

 hapalidioides Crouan et Crouan (1867) Type locality: 

 France 



6. Thalli 1 mm thick or less; perithallium cells mostly 8 to 

 12 jjL long; tetrasporangial conceptacles 250 to 500 ju. in 

 diameter . . . D. rasile (Foslie) Foslie (1909) = Litho- 

 phyllum (Dermatolithon) rasile Foslie (1907) Type lo- 

 cality : Tahiti 



7. Surface of crust irregular, warty or papillate 9 



7. Surface of crust more or less smooth ; hypothallium cells very 



variable in length 8 



8. Perithallium cells 6 to 15 /x long; tetrasporangial concep- 

 tacles 120 to 250 p. in diameter, sub-hemispherical . . . . D. 

 conspectum (Foslie) Foslie (1909) = Lithophyllum (Der- 

 matolithon) conspectum Foslie (1907a) Type locality: 

 Tierra del Fuego 



8. Perithallium cells 10 to 35 /x long ; conceptacles 150 to 200 /a 

 in diameter, not prominently elevated .... 2). saxicolum 

 (Lemoine) Setchell and Mason (1943) = Lithophyllum 

 (Dermatolithon) saxicolum Lemoine (1929) Tj'pe local- 

 ity: Cocos Island, Costa Rica 



9. Thalli 1 to 2 mm thick, not extensively superimposed; hypo- 

 thallium cells mostly 25 to 60 [x long 10 



