Marine Algae from Eniwetok — DAWSON 
Fig. 23. a, Dicranema rosaliae : Transection of a 
branch to show central core of small cells (after Setchell 
and Gardner), b, Coelothrix irregularis-. Habit of part of a 
tetrasporic plant of D. 13782 with stichidia, X 10. 
ramulis lateralibus determinantibus regulariter 
distichis ex cellulis axilaribus omnibus salien- 
tibus 60-120 fx longis adscendenti-curvatis et 
in latere adaxilare ramulis determinantibus 
secundariis productis, apicibus ramorum ob- 
tusis, tetrasporangiis ca. 20 g diametro tri- 
partite sessilibus sparsis e latere adaxiali 
cellulae inferioris ramulis lateralibus pro- 
ductis. 
type: Dawson 13633, forming tufts on 
crustose coralline algae near the outer margin 
of the seaward reef opposite EMBL, Parry 
Island, August 19, 1955. 
This plant is related to Antithamnion 
pteroton Schousb. ex Bornet, but is a markedly 
distinct species in its percurrent erect axes, 
its large, sessile sporangia, and the short, 
symmetrical pinnae lacking any abaxial sec- 
ondary branchlets. 
117 
Antithamnion hreviramosus var. simplex 
var. nov. 
Fig. 24c, d 
Like the type, but more delicate and slender 
with main axes only 25-30 \x in diameter, and 
with lateral branchlets simple or only once 
forked; axial cells longer, 6-8 (10) diameters 
long; attachment by a short, 1-2 celled rhiz- 
oidal outgrowth from the lowermost cell of 
a lateral branch. 
A typo simili sed axilibus principalibus 
tantum 25-30 \x diametro et cellulis longiori- 
bus 6-8 (10)-plo longioribus quam latis, 
ramulis lateralibus simplicibus vel unifurcatis. 
type: Dawson 13704a, creeping on Grijfith- 
sia tenuis from coral heads at a depth of 10 
feet in the lagoon, south end of Parry Island, 
August 21. 
This tiny plant is remarkably similar to that 
described from Santa Catalina Island, Califor- 
nia (Dawson 1949: 14, figs. 28, 57) and seems 
to be only a more delicate, lax, and less- 
branched variant of that species. 
Callithamnion marshallensis sp. nov. 
Fig. 25<2-c 
Thalli attached to other algae or to shells 
or debris, loosely tufted, 4-5 mm. high, 
consisting of an irregularly semi-prostrate 
part attached by modified lateral branchlets 
with adherent terminal discs, some of the 
attachment branchlets distinctly catenate in 
their cell form and unlike vegetative branch- 
lets; main axes 80-90 /jl in diameter, non- 
corticated, of cells I-IV 2 diameters long; 
lateral branchlets 20-30 g in diameter, lax, 
long, somewhat attenuate but terminally 
blunt, mostly simple, curved, alternate, but 
not always from every cell, mostly spirally 
arranged, often with approximately P5 diver- 
gence, but sometimes in part tending to be 
distichous; tetrasporangia tripartite, sub- 
spherical, about 40 ju in diameter, sessile and 
