NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 33 



Thalli epiphytic, consisting of a monostromatic basal stratum of 

 closely approximate cells, some of which penetrate slightly between the 

 host cells, and from which numerous branched, erect filaments arise; 

 erect filaments 600-800 //, long, 5-7 /x in diameter, of cells 2-4 times as 

 long as wide, with a stellate chromatophore and a single large central 

 pyrenoid situated in the distal portion of the cell; branching frequent, 

 mostly secund but in part alternate; reproduction by monospores and 

 tetraspores ; monosporangia ovoid, about 6 /x, in diameter, borne in secund 

 series usually on 1 -celled pedicels; tetrasporangia ovoid, alternate or 

 secund, sessile or on 1-2-celled pedicels, 7-8 a in diameter, occasionally 

 one or both pedicel cells also becoming tetrasporangia. 



Type: Holotype is Dawson 736-40, July 18, 1940, in vial 1122 

 and on slides 924-928 in HAHF. 



Type locality : Epiphytic on old Sargassum from intertidal rocky 

 reef at Isla Turner, Sonora, Mexico. 



Helminthocladiaceae 



Key to the Mexican Genera and Species 



1. Thalli more or less calcified; chromatophores discoid, parietal. 



Liagora 6 



1. Thalli uncalcified; chromatophores stellate 2 



2. Erect thallus parts simple or dichotomously branched, with- 

 out short lateral branchlets; gonimoblast filaments in a 

 compact mass, not growing between assimilating filaments 



Nemalion 4 



2. Erect thallus parts multifariously branched .... 3 

 3. Erect thallus parts bearing numerous short, mostly simple, 

 lateral branchlets; gonimoblast filaments widely divergent, 



growing between assimilating filaments 



Cumagloia andersonii 



3. Erect thallus parts indeterminately branched in 1-3 orders; 

 gonimoblast filaments compact, surrounded by a prominent 

 sterile involucre .... H ehninthocladia calif ornica 

 4. Thallus unbranched above the pulvinate base 



Nemalion helminthoides 



4. Thallus dichotomously branched 5 



5. Thallus 1-2 cm. high, densely branched; medullary filaments 

 10-13 /A in diameter A^. pulvinatum 



