10 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 26 



side (some of the latter often suppressed), all about the same length, 

 the tips sharply pointed, little attenuated; short determinate laterals 3-4 

 cells long, oppositely branched; gland cells on the ultimate branchlets, 

 lying along a single cell; tetrasporangia broadly ellipsoidal, sessile or 

 pedicellate, 25-34 jx long, 13-25 jx broad, on the long determinate 

 laterals; "gonimoblasts sessile on the upper branches;" spermatangia in 

 small clusters replacing ultimate branchlets of both long and short 

 determinate laterals. 



Type: Collections by Kylin not specifically designated, represented 

 by several syntypes probably to be found in the Agardh Herbarium at 

 Lund, Sweden. 



Type locality: Not specifically designated, cited as "San Juan 

 Island, on the piles of Friday Harbor's docks; Shaw Island and Canoe 

 Island, dredged at a depth of 10-20 meters." 



Mexican distribution: Pacific Baja Calif. — D. 9751. Bahia 

 Blanca, 18-30 m.; D. 1574, D. 1613, near Punta Maria. Some of the 

 latter specimens have dwarf laterals more than half as long as the long 

 laterals and, with considerable suppression of the abaxial branchlets, 

 give much the impression of P. intermedium Tokida. 



A Working Key to the North Pacific Species of Antithamnion 



1. Primary determinate branches essentially in opposite pairs 2 



1. Primary determinate branches in whorls of 3 or 4 35 



2. Some opposite pairs of determinate branchlets with one 



member commonly suppressed 3 



2. Determinate branchlets mostly in regular opposite pairs, 



rarely with suppression of one member of a pair 4 



3. Plants slender and fragile, the main axes 60-75 ju, in diam. 



A. gardneri G. DeToni (this 



species is apparently equivalent to A. spirographidis Schiffner) 

 3. Plants relatively rigid, coarser, the main axis 125-140 /x in 



diameter A. asymmetricum Gardner 



4. Determinate branches compound, that is, with secondary 



branchlets on one or both sides 5 



4. Determinate branches mainly simple, seldom with secon- 

 dary branchlets on one or both sides 28 



5. Secondary determinate branchlets predominately pectinate or 



secund 6 



5. Secondary determinate branchlets predominately pinnate or 



forked 20 



6. Gland cells present 7 



6. Gland cells absent (or at least not reported) 14 



