Pl. cell. aph. 2. THALASSIOPHYT . 75. Halidrys. 391 
L. 75. HALIDRYS. Lyngbye. Sea-oak. 
Thallus compressed, confluent, forked, ribless ; vesicles 0, 
or innate; holdfasts shieldlike: sporidia intermixed with 
jointed fibres in roundish thece immersed in pedicelled, 
lateral apothecia. 
1. Halidrys nodosa. Knobled sea-oak. 
Thallus pinnately branched. 
Fucus maritimus nodosus, Rati Syn. 48, 4). 
Fucus nodosus, Lin. S. P. 1628; Engl. Bot. 570; Turn. Hist. 91. 
Halidrys nodosa, Lyngbye Hydr. Dan. 37. 
Sea-shore; perennial; winter. 
Thallus 3 or 4 feet long, flat; apothecia roundish, mostly 
solitary. 
8. minor. Apothecia ovate, hardly wider than the pe- 
duncle. 
y. siliquatus. Apothecia linear, lanceolate. 
2. Halidrys canaliculata. Channelled sea-oak. 
Thallus compressed, ribless, linear, grooved on one side, 
level-topped; edge not cut; tip 2-cut; apothecia oblong, 
2-cut, turned. 
Fucus pumilus dichotomus, segmentis ex una parte gibbosis, ex altera 
excavatis, Rati Syn. 43, 12. 
Fucus canaliculatus, Linn. Syst. Nat.116; Engl. Bot. 823; Zurn. Hist. 3. 
Fucus excisus, Lin. S. P. 1627. 
Fucus rotundus, Esper, 17. 
Sea-shore; perennial. : 
Thalli aggregate, 2 to 4 inches long. 
3. Halidrys Mackai. Mackay’s sea-oak. 
Thallus leatherlike, cylindrical, threadlike, forked, level- 
topped; éips blunt; vesicles scattered, innate, elliptical, 
solitary, wider than the thallus. 
Fucus Mackaii, Zurn. Hist. 52; Engl, Bot. 1927. 
Sea-shore; perennial; winter. 
Thallus 6 to 12 inches high, lower part compressed ; 
angles of the fork roundish. 
LI. 71. MACKATA. Mackay. 
Thallus cartilaginous, rod-like, shrubby; upper part 
branched, narrow, roundish compressed, below compressed, 
broad, leaflike; holdfasts shieldlike; vesicles 0, or innate 
in the branches; sportdia in roundish thece intermixed 
with jointed fibres, or in terminal apothecia. 
