254 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



Grateloupia hancockii Dawson 

 PI. 1, figs. 7-8 



Dawson 1944, p. 280, pi. 69, fig. 2; Dawson 1950, p. 155. 



Thalli, as usually found growing on intertidal rocks, forming dark 

 greenish or brownish clumps 2-3 cm. high, sometimes of looser form 

 and to 7 cm. high when growing in protected pools, consisting of several 

 to many erect, much-branched, mostly non-percurrent axes from a dis- 

 coid holdfast, coriaceous when dry; erect parts compressed to flattened, 

 narrow, mostly 0.5-1.0 mm. wide in mid-parts, 300-400 (or to 700) 

 fji thick, branched throughout ; branching of 2-3 orders, multifarious, but 

 often appearing predominantly pinnate, mostly irregular, the ultimate 

 branches ± acute, less than 0.5 mm. wide, sometimes attenuated; me- 

 dulla of slender, branched filaments, sparse and interlacing toward the 

 center, denser and mostly longitudinal next to the subcortex; cortex 

 7-8 cells thick, the 1-2 inner layers of larger cells (12-15 fx) bearing 

 anticlinal filaments of small, pigmented cells (5 fi or less) ; tetraspor- 

 angia scattered through the essentially unmodified cortex just below the 

 surface; gonimoblast development characteristic of the genus; cysto- 

 carps scattered throughout the thallus, not especially aggregated ; anther- 

 idia borne in an indeterminate superficial layer from somewhat nema- 

 thecially modified outer cortical cells. 



Type: Holotype is Dawson 650-40, July 15, 1940, on sheet 30 in 

 HAHF. 



Type locality: Middle littoral rocks on headland three miles 

 north of Kino, Sonora, Mexico. 



Mexican distribution: Sonora — D. 711-40 (young 0), Isla 

 Turner, Jan.; D. 1648 (d), near Cabo Arco, May; D. 1765 (?), 

 Bahia Bocochibampo, May; D. 1843 (d), Ensenada de San Francisco, 

 May. 



The fertile material now available marks this plant distinctly as a 

 species of Grateloupia. Its nearest apparent relative is G. avalona Daw- 

 son, from Santa Catalina Island, California, which is similar in habit, 

 color and structure, but has among its differences a medulla of cells 

 whose exceedingly hygroscopic walls cause sections of dry material to 

 turn inside out when placed in water. Such a feature has not been noted 

 in G. hancockii. 



From small clumping examples of Grateloupia filicina in the Gulf of 

 California area, G. hancockii is distinguished by the distinctly non-hollow 

 medulla and the stiffer, relatively coarse branches. 



This species appears commonly to be the host of endophytic Cal- 

 lithamnion endovaginum S. & G. 



