244 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



2. Medulla narrow to very broad, not dense, but consisting 

 of loosely arranged to sparse filaments in a soft jelly, or 

 sometimes a hollow or nearly so; tetrasporangia not in 



nemathecial sori 4 



3. Thalli with determinate or indeterminate secondary pinnate 



branches upon which the nemathecial tetrasporic sori are borne 



(in some species also on terminal segments) Zanardinula p. 275 



3. Thalli mainly dichotomously branched, without prominent 



secondary pinnae; tetrasporic nemathecia borne near apices of 



terminal segments Polyopes p. 265 



4. Medullary filaments prominently or dominantly anti- 

 clinal (sometimes oblique), many extending across the 

 medulla from cortex to cortex . Halymenia p. 267 

 4. Medullary filaments intertwining and mostly longitudin- 

 ally arranged 5 



5. Cortex thin, of 2-3 layers of angular to rotund cells, not show- 

 ing any arrangement as anticlinal filaments; thallus generally 



not lubricous Cryptonemia p. 259 



5. Outer cortex composed of very small cells arranged in anti- 

 clinal filaments; thallus generally lubricous Grateloupia p. 244 



Key to the Mexican Species of Grateloupia 



1. Medullary filaments mostly 5-7 /a in diam., mostly of cells 

 many times as long as wide; dry material expanding readily in 



water 2 



1. Medullary filaments mostly 15-20 ju, in diam., mostly of cells 

 only a few diameters long; dry material expanding poorly in 



water; reproduction unknown 11 



2, Broader erect thallus parts 6 mm. or less in width . . 7 

 2. Broader thallus parts more than 6 mm. in width . . 3 



3. Thalli simple, 10-30 cm. wide G. maxima 



3. Thalli usually branched, 1-6 cm. wide 4 



4. Blade surfaces smooth or bearing proliferous branchlets 5 

 4. Blade surfaces covered with spinose, gigartinoid papil- 



lations G. howei 



5. Uninjured blades normally simple or once or twice divided, 



not pinnate unless proliferously so 6 



5. Uninjured blades normally pinnate . . . G. prolongata 



