IV. 
DICTYOTACEiE. — Padina. 
103 
1. Halisekis delicatula , Lamour. ; frond delicately membranaceous, winged from 
the base, dichotomous ; with very patent linear segments and rounded angles ; 
the margin very entire, somewhat thickened. J. Ag. Sp. Alg. 1, p. 11 6. Kiitz. 
Sp. Alg. p. 562. (Tab. YII. A.) 
Hab. On the shores of Mexico, J. Agarclh. (v. s. in Herb. T.C.D.) 
Fronds densely tufted, three or four inches long, and from one to two lines in 
breadth, thrice or four times forked, the forkings an inch or more apart, widely 
spreading or divaricate, and somewhat flexuous. Segments linear, obtuse, with an 
entire, slightly thickened margin, distinctly marked by a depressed line, and formed 
of smaller and more vertical cells than the interior portion of the membrane. 
Sori minute, oblong, forming a line at each side of the midrib. Substance very 
thin and delicate, composed of oblong cells, ranged in series proceeding obliquely 
from the midrib to the margin. Colour very pale, greenish-olive. I have not seen 
Mexican specimens, and have taken this description and prepared the figure given ? 
from specimens collected at Pernambuco, and presented by Dr. Areschoug, to the 
Herbarium of the University of Dublin. 
Plate YII. A. Fig. 1 . Plant of Haliseris delicatula; the natural size ; jig. 2, 
a segment, slightly magnified ; jig. 3, a small portion of the same, with a sorus ; 
fig. 4, spores : both more or less highly magnified. 
II. PADINA. Adans. 
Boot coated with woolly hairs. Frond flat, ribless, fan-shaped, marked at regular 
distances with concentric lines, and fringed with articulated hairs ; the apex invo- 
lute. Fructification , linear, concentric sori , formed beneath the cuticle of the upper 
surface of the frond, and bursting through it ; and containing at maturity, numer- 
ous obovate, hyaline perispores fixed by their bases, each perispore enclosing four 
spores. Paranemata club-shaped, articulate, disposed in concentric lines alternating 
between the sori. 
Four species of this genus are retained by Agardh, who admits the difficulty of 
distinguishing them by exact characters. All have very similar fronds, all inhabit the 
warmer parts of the sea, and P. Pavonia at least is subject, even in the same locality, 
to variations almost as great as those which have been fixed on by authors, as 
characteristics of the several supposed species. But if there be a difficulty in 
distinguishing these plants, supposing them to be really different in specific charac- 
ter one from another, there is none in recognising our common species among all 
