274 DAWSON 



9. Thalli 50 to 225 ju, thick, the crusts much superimposed . . . D. 

 papillosum (Hauck) Foslie (1909) van papillosum = Litho- 

 thamnion papillosum Zanardini ex Hauck (1885) Type local- 

 ity: Adriatic Sea 



10. Thalli producing warty excrescences; tetrasporangial con- 

 ceptacles 300 to 400 /a in outside diameter ; plants gro\\-ing 

 on shells . . . D. polycephalum (Foslie) Foslie (1909) 

 = Lithophyllum polycephalum Foslie (1905) Type local- 

 \ty: Cape Verde Islands 

 10. Thalli uneven, usually assuming the form of the substrate 

 but without warty excrescences; tetrasporangial concep- 

 tacles 400 to 600 ju. in outside diameter, sometimes over- 

 grown; plants growing on calcareous pebbles . . . . D. 

 bermudense (Foslie and Howe) Foslie (1909) = Litho- 

 phyllum bermudense Foslie and Howe (1906) Type lo- 

 cality : Bermuda 

 11. Thalli with more or less extensive monostromatic areas, at least 

 around the margins ; perithallium usually of four or fewer layers 



in mid-parts 12 



11. Thalli polystromatic throughout, or up to the thallus edges; 



perithallium of 5 to many layers in mid-parts 17 



12. Thalli mammillate, the surface provided with warty pro- 

 tuberances; conceptacles little elevated . . . D. papillosum 

 var. cystoseirae (Hauck) Lemoine (1924) = Melobesia 

 cystosirae Hauck (1885) Type locality : Adriatic Sea 

 12. Thallus more or less smooth, without warty protuberances 13 

 13. Crusts overlapping and superimposed; monostromatic parts ex- 

 tensive; conceptacles little elevated . . . D. prototypum var. 

 udoteae (Foslie) comb. nov. = Goniolithon udoteae Foslie 

 (1901a) Type locality : West Indies 

 13. Crusts not extensively superimposed; conceptacles protruding, 



hemispherical to subconical I't 



14. Thalli commonly over 120 /^ thick, at least in older parts, 



the perithallium of 1 to several cell layers 15 



14. ThalH usually less than 120 p. thick even in older parts, 

 the perithallium little developed ; hypothallium cells short, 

 25 to 60 I), long; tetrasporangial conceptacles 300 to 350 }x 

 in outside diameter . . . . D. canescens (Foslie) Foslie 

 (1909) = Melobesia (Heteroderma) canescens Foslie 

 ( 1900) Type locality: Japan 



