NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 35 



Mexican distribution: Pacific Baja Calif. — D. 8299 (62-66 m.), 

 D. 8261, D. 8423, D. 8434, D. 8435, D. 8436 (45-53 m.), D. 8460 

 (73 m.), Isla Guadalupe. Revillagigedo Arch. — Taylor 39-66B, Isla 

 Socorro. 



Callithamnion uncinatum sp. nov. 

 PI. 11, fig. 4 

 Thalli fruticulosi, ad 14 mm. alt., per massam rhizoideorum ramosorum 

 multicellularium affixi; axes primarii erecti et multi, saepe plus minusve 

 distiche ramosi, ecorticati nisi prope basim per rhizoidea sparsa descendentia 

 plus minusve appressa; axes primarii ad 150 fi diam., e cellulis in partibus 

 inferioribus 1.5-2.5 /j. longioribus quam latae, supra brevioribus compositi; 

 rami laterales determinantes plerumque distichi ca. 1-1.3 mm. long., ca. 60 /t 

 diam, ad basim cum maturi, attenuati sed obtusi, primum prominenter forcipati 

 et super cellulam apicalem arcuantes, cacuminibus mox rectis deinde recurvatis 

 uncinatisque factis; tetrasporangia in latere adaxiali ramulorum lateralium 

 seriata, sessilia ovata, 40-45 /x long., 23-26 /i lat.; reproductio sexualis non visa. 



Thalli tufted, to 14 mm. high, attached by a mass of multicellular, 

 branched rhizoids; erect primary axes numerous, frequently more or 

 less distichously branched, uncorticated except by sparse, descending, 

 dz appressed rhizoids near the base; primary axes to 150 jx in diam., 

 of cells 1.5-2.5 diameters long in lower parts, shorter above; determinate 

 lateral branches essentially distichous, about 1.0-1.3 mm. long, about 

 60 jx in diam. at the base at maturity, tapering, but blunt, prominently 

 forcipate and overarching the apical cell at first, the tips soon straighten- 

 ing, then becoming recurved and uncinate; tetrasporangia seriate on the 

 adaxial side of lateral branchlets, sessile, ovoid, 40-45 jx long, 23-26 jx 

 broad; asexual reproduction not seen. 



Type: Holotype is E. Y. Dawson 3814, January 10, 1947, in 

 Herb. Beaudette Foundation. 



Type locality: Surfy, granitic headland south af Salina Cruz, 

 Oaxaca, Mexico. 



Additional material: D. 3779, D. 3781, vicinity of Salina 

 Cruz, Oaxaca, Jan. 9, 1947. 



This species is closely related to C. rupicolum, but differs in the 

 overarching, forcipate laterals at the tips, the uncinate character of 

 mature laterals, and the smaller tetrasporangia. 



Key to the World Species of Aglaothamnion 

 1. Thalli less than 1 mm. high, attached by a single, partially 



endophytic basal cell A. monopodum Borg. 



1. Thalli 4 mm. high or more, attached by multiple rhizoids 2 



2. Branching alternate, spiral, multifarious, becoming subdicho- 



tomous above 3 



2. Branching alternate and pinnate, at least in the upper parts 7 



3. Branchlets often terminating in a hair 4 



3. Branchlets not terminating in a hair 5 



