NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 63 



Guadalupe on the north to Salina Cruz, Oaxaca on the south. It has been 

 found both in intertidal and sublittoral situations on a variety of different 

 substrates. 



Several variations are represented in the present material, most of 

 which seem to fall within the limits of var. minusculum Weber van 

 Bosse, var. mucronatiim Dangeard, var. conchicola Pice. & Grun,, and 

 var. pulvinatum (Ag.) Feldmann. A few specimens show the nearly 

 simple, terete erect branches and terminal tetrasporangial sori of var. 

 cylindricum Taylor. 



Gelidium sclerophyllum Taylor 



Taylor, 1945, p. 156, pi. 5, fig. 13, pi. 33, fig. 2. 



Thalli 0.6-2.0 cm. high, growing on barnacles, fixed mollusks or 

 crustose corallines, more or less densely tufted, consisting of numerous 

 erect, flattened fronds from creeping branches attached at close intervals 

 by peg-like haptera ; erect fronds terete or compressed at the base, ligu- 

 late above, to 1 mm. wide, subsimple or irregularly once pinnate, or pro- 

 liferous, the branchlets constricted at the base; apices of fertile branch- 

 lets commonly deeply indented ; transection showing a row of thick- 

 walled cells across the width of the blade, these separated and surrounded 

 by closely packed rhizoidal filaments which become more scattered in the 

 subcortical area ; large, thin-walled cells absent from the medulla ; tetra- 

 sporangial sori occupying the central area of lateral or terminal branch- 

 lets the margins of which are sterile and thicker when dry; cystocarps 

 400-500 /A in diameter, borne near the ends of terminal or lateral branch- 

 lets. 



Type: Holotype is Taylor 34-489, Feb. 11, 1934, on sheet 160 in 

 HAHF. 



Type locality: At a depth of 5.4 meters with corallinae, near the 

 northeastern limit of Bahia San Francisco, Esmeraldas, Ecuador. 



Mexican distribution: Baja Calif. — D. 6818 (Mar.), D. 3395 

 (Nov.), Cabeza Ballena, tttrzs^oric. Stnaloa — D. 3624, Mazatlan, 

 Dec, tetrasporic. Revillagigedo Archip. — Howell 492, Isla Clarion, 

 Mar. Jalisco — D. 3728c, Barra Navidad, Dec, cystocarpic Guerrero — 

 D. 3858, 3929, Acapulco, Feb., tetrasporic. Oaxaca — D. 3823, Salina 

 Cruz, Jan., tetrasporic. 



The indented tips of fertile branchlets, the sterile margins of tetra- 

 sporangial branchlets and the dense structure of thick-walled cells in the 

 medulla mark this small Gelidium as distinct. 



