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144 Rhodora [AucusT 
II. A NEW ERYTHROTRICHIA FROM Woops HOLE. 
Erythrotrichia rhizoidea, n.sp. Thallus filamentoso-teres, roseus 
v. roseo-purpureus, rectus, 1-4 mm. longus, 10-50 u diametro. Basis 
rhizoidalis, ex qua breves recti thalli secundarii nascuntur. Sporae 
roseae, 8-10 u diametro. 
Thallus dark red to reddish-purple, upright, terete, 4 mm. long at 
most, usually 1-2 mm. in length; 10 in diameter at base, increasing 
to 40-50 u above; dividing at base into several short, irregularly 
down-growing rhizoidal filaments, which penetrate into the tissue of 
the host, and from which arise often one or more secondary thalli, 
rarely approaching the primary thallus in length, usually much shorter. 
Cells roundish-polygonal, 10-20 u in diameter, dividing above in 
both horizontal planes into 4-8 cells. Spores reddish, 8-10 u in 
diameter. Sexual organs not observed. Growing on Porphyra 
umbilicalis in the harbor of Woods Hole, Mass. Abundant. August, 
1917. 
This species differs from E. Bertholdii Batt. (= E. ciliaris Berth., 
but not Bangia ciliaris Carm., according to Batters) ! in its smaller 
size, the presence of secondary upright thalli, and the rhizoidal nature 
of the holdfast. E. Bertholdii Batt. is attached merely by its slightly 
expanded basal cell. 
It differs from E. discigera Berth., in that it has no definite basal 
dise as holdfast, and the holdfast is never seen without filaments 
attached. 
Differs from Æ. ciliaris Batt.,! the species that Batters considers to 
be the original Bangia ciliaris of Carmichael, in the absence of a basal 
disc. In Æ. ciliaris, also, the erect filaments all appear to be of about 
the same strength and length. In our species, however, only one 
filament attains to any length, the others, when there are others, 
being usually very short. 
E. obscura Berth. does not fit our species in the following respects :— 
1. Its blackish color. 2. When there are more than one series of cells, 
they lie in one plane. 3. The erect frond may have branches at the 
base, but no rhizoids. 4. The holdfast is in the nature of a basal 
disc. 5. In summer, the basal discs are very usually found bearing 
no erect filaments. 
1 Batters, E. A. L. New or Critical British Marine Algae. Journal of Botany, Vol. 38, pp. 
369-379. 
2 Berthold, G. Die Bangiaceen des Golfes von Neapel. Fauna u. Flora des Golfes von 
Neapel, Vol. VIII, Leipzig, 1882. 
