GRASS-GREEN SEAWEEDS 59 
Hi. tridens. Fronds solitary, erect; base composed of confluent 
articulations ; above divided into numerous branches of articulations, 
which are all flat, and in one plane giving a fan-shaped outline; middle 
joints wedge-shaped; upper ones divided into three lobes, frequently 
bearing articulations at the summit of each lobe; thinly incrusted with 
lime; color bright green. (Plate VII.) 
H. opuntia. Articulations kidney-shaped, flat, rather thin ; margins 
scalloped; irregularly branched and spreading; dense tufts. 
ORDER CODIACEA 
Genus Bryopsis 
(‘' Moss-like”’) 
There are said to be about twenty species of this genus. They 
are distinguished by the manner of branching, but are not very 
definitely marked. All are erect, one-celled, branching stalks, 
and are feather-like in appearance. 
B. plumosa. Fronds branched twice or more; branchlets or pin- 
nules tapering as they rise on the stalk, giving a triangular outline; 
stalk naked below; plants a vivid dark green in color, two to six inches 
long, growing in tufts on wharves and stones at low-water mark and in 
tide-pools. It is common along the whole Atlantic and Pacific coasts. 
It is well to use salt water for mounting this alga, since the green color- 
ing-matter or granular endochrome with which it is filled easily escapes. 
(Plate VII.) 
Genus Codium 
C. tomentosum. This is called the commonest seaweed in the world. 
It is abundant in every latitude, yet it does not appear on the eastern 
coast of North America. It is found on the gulf coast of Florida and 
is plentiful on the Pacific coast. The fronds are often a foot long, com- 
posed of closely packed, club-shaped branches dividing in a forking 
manner, and densely covered with fine filaments which give them a soft, 
sponge-like texture. (Plate VII.) 
ORDER CAULERPACEE 
Genus Caulerpa 
(From two Greek words meaning ' stem" and ‘creep ”’) 
Caulerpa is the only genus of its order, but it contains about 
a hundred species, many of which resemble mosses, ferns, or cacti. 
Each plant is composed of a single cell, however much it may be 
