NO. 2 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 281 



proliferis determinatis, pinnatis, essentialiter distichis, plerumque 2-3 

 mm. longis, lanceolatis, simplicibus vel furcatis ; tetrasporangiis in cortice 

 nemathecialiter modificata ramulorum determinatorum contentis. 



Thalli erect, loosely bushy, up to 20 cm. high, consisting of several 

 much-branched, compressed to flattened axes somewhat less than 1 mm. 

 wide, 300-450 fi thick, from a coarse, firmly attached discoid holdfast; 

 branching of main fronds initiated in an irregularly dichotomous to 

 subpinnate manner near the base of primary axes, these branches in- 

 determinate and subsequently branching dichotomously at intervals of 

 2-4 cm., sometimes more approximate above; secondary proliferous 

 branching determinate, pinnate and essentially distichous, irregularly 

 spaced, sparse on some axes, on others numerous and closely spaced in 

 groups at intervals of 1-2 mm., mostly 2-3 mm. long, lanceolate, simple, 

 or sometimes forked, or bearing 1 or several minute tertiary branchlets ; 

 transection of main branches showing a rather thin outer cortex of anti- 

 clinal rows of about 3 small, squarish cells, a distinct subcortex of larger, 

 rotund cells and a dense medulla of compacted filaments about 5 /x in 

 diameter; tetrasporangia borne in the nemathecially modified outer 

 cortex of the determinate secondary pinnate branchlets, cruciate, 23-32 

 ju. long, 12-14 fji wide; sexual reproduction not seen. 



Type: Holotype is Dawson 10362, Nov. 1, 1951, on sheet 59306 

 in HAHF. 



Type locality: Intertidal rocky shore, Punta San Eugenio, be- 

 tween the lighthouse and the village, Baja California, Mexico. 



Additional material: D. 10014, Punta Velero, Bahia Vizcaino, 

 Baja California, Apr. 16, 1951. 



This species is somewhat similar to Zanardinula filiformis, especially 

 with the more slender form such as occurs at Monterey, California. It is, 

 however, more richly branched, especially below, and near the base is 

 often not regularly dichotomous. Z. vizcainensis is also smaller and 

 narrower throughout than Z. filifor?}iis. Although the differences be- 

 tween the two species seem mostly to be quantitative, one notes that the 

 distribution of Z. filiformis from Coos Bay, Oregon to central California 

 is that of a cool-water species. It is not known to occur south of Carmel 

 Bay. Z. vizcainensis, on the other hand, inhabits the southwest shore of 

 Bahia Vizcaino which is bathed by the warmest shore water known to 

 occur along Pacific Baja California. It seems highly probable that further 

 study of these two species will reveal additional differences reflecting 

 their habitat differences. 



