266 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 12 



PLATYTH AMNION J. Agardh, 1892 



Plants bushy, filamentous, the branching complanate, monosiphonous, 

 ecorticate; primary branching irregular, that on the main axes whorled 

 in fours, 2 lateral branchlets in the plane of the frond elongate, 2 branch- 

 lets on the faces rosette or spurlike and on the lesser branches not devel- 

 oped ; sporangia near the bases of the branchlets, tetrapartite; cystocarps 

 near the bases of the branchlets, without special involucre. 



KEY TO SPECIES 



1. Lateral branchlets on the adaxial side of the lesser branches larger 

 P. pectinatum v. laxum 



1. Lateral branchlets subequal, or those on the abaxial side of the 

 lesser branches larger P. reversum v. laxum 



Platythamnion pectinatum Kylin, v. laxum n. v.^^^ 



Plants delicate, lax, somewhat entangled, the main axis to 200 fi diam., 

 the cells to 600-650 fx long, bearing whorls of determinate branches on 

 the upper quarter; determinate branchlets in 4 rows, the lateral longer, 

 those on the faces ("transversal") smaller, sparingly branched and not 

 rosettelike; lateral determinate branches bearing branchlets on the upper 

 or adaxial side in two indefinite rows, these branchlets occasionally di- 

 vided, about 21 fi diam. at the base, the apices acute; prominent gland 

 cells commonly present near the upper ends of the branchlets in the 

 younger portions of the plant. 



These plants show little of the complanate habit of Platythamnion, 

 but the attenuation and laxness may be due to the depth at which they 

 grew. As they are sterile, the writer associates them with P. pectinatum 

 Kylin (1925, p. 53, figs. 32d, 33e, 34a-c), with which they agree in the 

 arrangement of the ultimate branchlets. 



Mexico: Is. Revilla Gigedo, dredged in abundance at sta. 135 from 

 46 meters' depth at Sulphur Bay, I. Clarion, no. 34-43 (TYPE), 5 Jan. 

 1934. 



1G6 Platythamnion pectinatum v. laxum n. v. — Planta laxa, axe primario ad 

 200 (x diam., cellulis ad 600-650 |.i long., ramos determinates in 4- ordinibus habens, 

 ramis transversalibus parvis, sparse divisis, ramis lateralibus longioribus, ramulos 

 in latere adaxiali ferentibus; ramulis circa 21 \i diam., saepe glandicellulas promi- 

 nentes 20 \i diam. prope partem superiorem habentibus; apicibus acutis. Planta 

 typica in loco dicto I. Clarion, Mexico, legit W. R. Taylor no. 34-43, 5 Jan. 1934. 



