58 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



it is less commonly encountered, having been found in the lowermost 

 littoral only at Isla San Francisco and at Bahia Agua Verde. Revillagi- 

 gedo Arch. — Taylor, 39-44, Bahia Sulphur, Isla Clarion, Mar. 



Sporophyte generation 

 (Falkenbergia hillebrandii (Bornet) Falk.) 



Thalli minute, filamentous, entangling, among other small algae, 3-5 

 mm. long, without a primary axis, irregularly and rather distantly multi- 

 fariously divaricately branched, 2.5-3.5 ju, in diameter, consisting of a 

 central axial filament surrounded by 3 pericentral cells which are about 

 twice as long as broad ; apex with a single prominent apical cell cutting 

 off lens-shaped cells basally, without trichoblasts; tetrasporangia in dis- 

 continuous rows (not observed in Mexican material) each formed by 

 direct transformation of one of the 3 pericentral cells of a segment. 



Type: Holotype not designated, but probably represented in Herb. 

 Bornet, Natural History Museum, Paris, by part of a collection by 

 Toscanelli, September. 



Type locality: "Tirreno all' Isola d'Elba," Italy. 



Mexican distribution : Pacific Baja Calif. — On Codium, Mason 

 128, Isla Guadalupe, Apr. (Herb. Calif. Acad. Sci.) ; D. 9939a, 10295, 

 10432, 10-17 miles west of Punta Malarrimo, Bahia Vizcaino, Apr., 

 Nov. Nayarit — D. 3701, Mira Mar, Dec. Guerrero — Hubbs 46-239, 

 Puerto Marques, Sept. 



Gelidiaceae 



Key to the Mexican Genera and Species 



1. Plants minute, spherical, colorless parasites . Gelidiocolax 



1. Plants not minute, spherical, colorless parasites .... 2 



2. Apices with a distinct apical cell, at least in youth . . 3 



2. Apices without an apical cell 27 



3. Thalli with rhizoidal filaments in the medulla and (or) in the 



subcortex 4 



3. Thalli without rhizoidal filaments .... Gelidiella 24 



4. Cystocarps bilocular Gelidiurn 5 



4. Cystocarps unilocular Pterocladia 21 



5. Plants very small, normally less than 2 cm. high ... 6 



5. Plants larger, normally more than 2 cm. high .... 8 



6. Rhizoidal filaments interlaced in all directions 



G. microphysa 



6. Rhizoidal filaments straight 7 



