272 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 3 



Genus HETERODERMA Foslie 

 Heteroderma Gibbsii (Fosl. & Setch.) Fosl. 



Foslie, 1909, p. 56. Melobesia Gibbsii Foslie & Setchell, in Foslie, 1907, 

 p. 26. 



Lacking a satisfactory figure of the characters of the type material, the 

 description has been expanded and clarified as follows by Mason (un- 

 published thesis manuscript) : 



Thallus crustaceous, epiphytic upon Sargassum, Dictyota, Padina, 

 etc., suborbicular at first, later irregular with adjacent thalli confluent, 

 partially monostromatic ; cells square, 7-12 [i diam., or elongated parallel 

 to the substratum, 11-16 /x long by 6-12 ju, broad ; cover cells rarely present 

 in the central portion of the thallus, a hypothallic layer often present, one 

 cell thick, with cells 2-4 ju, high by 6-10 /a broad, variable; heterocysts 

 absent in the thallus; sporangial conceptacles subconic, 250-300 /* in 

 diam.; antheridial conceptacles 40-50 fx diam., 12-16 ju. high; cystocarpic 

 conceptacles 140-160 fi diam., 40-70 fx high. 



Gibbs, 20-21, San Jose and Espiritu Santo islands, growing on Sar- 

 gassum; H. 4, growing on Padina, dredged in 40 m., off San Jose del 

 Cabo, Aug.; H. 9, same, on Dictyota; D. 217a, on old Padina, on shore, 

 Puerto Refugio, Jan. 



Before this alga was critically studied, it was called Melobesia tenuis 

 by W. A. Setchell, and as such was sent to Foslie, who upon superficial 

 examination at first considered it to be a form of M. farinosa. Later, how- 

 ever, he studied it in greater detail and found that in the size of cells and 

 size and form of conceptacles it did not agree with either AI. farinosa or 

 any other known Melobesia; so he named it M. Gibbsii. When Melobesia 

 was split up into two subgenera, it fell into the Heteroderma group. Upon 

 the raising of Heteroderma to generic rank, it became Heteroderma 

 Gibbsii. 



Heteroderma corallinicola sp. nov. 

 Plate 63, Fig. 2 



Frondes tenues, minutae, crustas ad superficies raraorum vetustorum. Coral- 

 linae arete adhaerentes, monostromaticae tantura in partibus margine plerumque 

 2-4 stratis cellularum cuboideis 9-14 \i diam., compositae; heterocystis deuntibus; 

 conceptaculis cystocarpiiferis aut immersis aut leviter prominentibus, 60 \i diam. ; 

 conceptaculis spermatangiiferis tetrasporangiiferisque nondum visis. 



Thallus thin, minute, forming closely adherent crusts over surfaces of 

 old branches of Corallina; very inconspicuous except when fruiting; 

 monostromatic only in marginal parts, usually of 2-4 layers of square 



