IV. DICTYOTACE^.— Padina. 103 



1. Halisekis delicatida, 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. 116. Kiitz. 

 Sp. Alg. p. 562. (Tab. VII. A.) 



Hab. On the shores of Mexico, /. Agardh. (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. Stibstance^ 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 VII. A. Fig. 1. Plant of Haliseeis delicatula; the natural size ; Jig. 2, 

 a segment, slightly magnified ; fig. 3, a smaU portion of the same, with a sorus ; 

 fig. 4, spores : hoVa. more or less highly magnified. 



II. PADINA. Adans. 



Root 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 mhabit the 

 warmer parts of the sea, and P. Pai'oma at least is subject, even m 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 difficu ty in 

 distinguishing these plants, supposing them to be really difterent in specific charac- 

 ter one from another, there is none in recognising our common species among all 



