NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 17 



at frequent intervals (sometimes from nearly every cell of the prostrate 

 part) by a multicellular uniseriate rhizoid about 30-40 /x in diameter 

 terminating in an irregular multicellular disc; primary axes 50-60 /m in 

 diameter, the cells 4-5 diameters long, with sparse indeterminate 

 branching but provided near the distal end of each cell with a pair 

 of spreading or somewhat ascending determinate branches; primary 

 determinate branches about 1 mm long, 30 /a in diameter near the 

 base, arising from a subspherical basal cell and provided with opposite 

 pinnate branchlets in their basal part and abaxially secund branchlets in 

 their distal part, the secondary branchlets simple or with a few abaxial 

 branchlets; all branchlets attenuated, essentially acute, of cells 2.0-2.5 

 diameters long; secondary indeterminate branches of the primary axis 

 arising from the subspherical basal cells of primary determinate 

 laterals; attachment rhizoids also commonly arising from this cell; 

 gland cells sparse, mostly on the secondary branches of the determinate 

 laterals, lying on two cells; reproduction unknown. 



Type: Holotype is E. Y. Dawson 8302, Dec. 19, 1949, in Herb. 

 Allan Hancock Foundation. 



Type locality: On Codium from a depth of 70 m., Melpomene 

 Cove, Isla Guadalupe, Baja Calif., Mexico. Additional material: D. 

 8311; D. 19295, 19297 (Carl Hubbs) dredged, Isla Guadalupe. 



This species is closely related to A. cristirhizophorum Tokida and 

 Inaba (1950). It differs mainly in the characters of the rhizoids which 

 are solitary from a node in the present species, rather than multiple and 

 compound. The determinate branches tend to be more attenuated and 

 to have longer cells. The gland cells usually adjoin two rather than 

 three cells. 



Antithamnion kylinii Gard. 

 PI. 6, fig. 1 

 Gardner 1927b, p. 411, pi. 89, fig. 1; Dawson 1954, p. 342. 



Thallus densely tufted, 2-3 (4) cm high, usually with a central 

 percurrent axis bearing several major branches; all branches giving 

 rise from near the distal end of each cell to paired, opposite, determinate 

 branches with 5-8 secund ultimate branchlets on the adaxial side; 

 indeterminate branches usually with an opposite simple determinate 

 branch; cells of main axes (80) 125-150 (170) [x in diameter below 

 and about 3 diameters long, cylindrical; determinate branchlets 12-15 

 cells long, tapering very gradually to acute apices, the basal cell being 

 subspherical, the others cylindrical to slightly doliioform; gland cells 

 on the ultimate branchlets, usually lying on two cells; tetrasporangia 

 usually on 1-celled pedicels, 1-3 on the adaxial side of the geminate 

 branchlets near the base, 40-70 /x long; sexual plants unknown (modified 

 after Gardner) . 



Type: Gardner 3904, June, in the Herbarium of the Univ. of 



