NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 19 



gradually reduced to the tips; secondary indeterminate branches 

 frequent, 3-4 segments apart, multifarious, usually without tertiary 

 intermediate branches; ultimate determinate branchlets whorled in 

 groups of three, short, about 100 p long, with two, three, or sometimes 

 four forks in a digitate manner, the first two usually of a single cell 

 each and the last sometimes of a single cell, sometimes of two, the cells 

 successively reduced in size to 10 p or less long and 6-7 p. wide at the 

 ends, the end of the cell blunt, subacute, or bearing a colorless hair; 

 gland cells absent; reproduction not seen. 



Type: Dawson 18855, April 20, 1958, in Herb. Los Angeles 

 County Museum. 



Type locality: Scraped from rock surfaces with other minute 

 algae from depths of about 3 feet, El Solitario rock, Bahia Agua Verde, 

 Baja California del Sur, Mexico. 



In size and superficial characters this tiny species suggests A. 

 breviramosus Dawson. The dense aggregation of axes matted together 

 with rhizoids, the absence of gland cells and the short-segmented, digitate 

 determinate laterals are, however, amply distinctive. 



Antithamnion pacificum (Harv.) Kylin 

 PL 4, fig. 8-9 



Kylin, 1925, p. 47. fig. 29; Dawson, 1944, p. 313; Smith 1944, p. 310. 

 Callithamnion flocossum var. pacificum Harvey 1862. p. 176. 



This species was reported by Dawson as occurring at Tepoca Bay, 

 upper Gulf of California, at a depth of 22 meters, and near Guaymas 

 at 30-36 meters. These specimens do not now appear in the Allan 

 Hancock Foundation Herbarium and are presumed misfiled. The verifi- 

 cation of this occurrence must await further collections. 



Antithamnion plumulum (Ellis & Solander) Thuret, ex Lejolis 



var. plumulum 

 PL 6, fig. 4 



Thuret, in LeJolis 1863, p. 112; Okamura 1922, pi. 189, p. 157. Conferva 

 plumula Ellis and Solander 1786, pi. 57, P : 426; Dillwyn 1809, pi. 50. 



Thalli minute, 1-3 mm or more in extent, consisting of a primary 

 axis 40-50 p in diameter; cells 1-1.5 diameters long below to 2 diameters 

 long above; indeterminate branches of the axis with an opposite deter- 

 minate branch; axes provided at each cell node with an opposite pair 

 of determinate branches 200-300 p. long of 6-9 elongated cells, at first 

 incurved, later somewhat recurved, bearing on their adaxial side 3-5 

 simple, somewhat attenuated, acute, ultimate branchlets; main axes 

 producing here and there 1 or a pair of short, spine-like determinate 

 branchlets in a plane perpendicular to the regular distichous laterals; 

 gland cells on ultimate branchlets, resting on a single cell; reproduction 

 not observed. 



