376 PERCY SLADEN TRUST EXPEDITION. 
been described as occurring in Iicrodictyon ; and we were therefore much interested to 
find that the apical attachment-points of the branchlets in our plant have the appearance 
of tenacula. We submitted our specimens to Major Reinbold, who has lately studied 
this genus and will shortly publish his conclusions in the reports of the ‘Siboga’ 
Expedition ; and he kindly pointed out that the attachment-points in our specimens are 
not true tenacula—that is, specialised cells—but are merely crenellated cell-ends (fig. 3). 
They are, however, of sufficient importance to warrant his placing our species in a 
separate section of the genus, a matter which he will deal with in his forthcoming paper. 
M. pseudohapteron may also be recognised by the ramification, which in mature parts 
of the thallus tends to be stellate at the nodes. This appears to arise in the following 
manner :—The main filaments at each transverse wall put out a pair of opposite branches 
in the same plane at right angles to the axis of the filament. Each of these branches is 
seen to be seated in a lateral notch, as shown in fig. 2, c. Subsequently these branches 
may become pulled or pushed forward so as to be situated at an acute angle with the 
apical part of the main filament. Usually a second branch emerges from the main 
filament in the axil below the first branch, and as it grows it tilts the first branch 
forward. Thus a stellate node is obtained (fig. 2, d), and this, as mentioned above, is 
characteristic of our species. Each branch repeats this mode of ramification more or 
less regularly, and the triangular or polygonal meshes become more and more subdivided, 
and sometimes almost filled in by the ultimate branchlets. As previously mentioned, 
the free ends of the branchlets become adherent to the sides of neighbouring cells, and 
thus the firm flat net of the thallus is formed. 
Though most of the other species have a cruciform ramification, yet some of the 
species show in the same thallus both cruciform and stellate modes of ramification. 
Major Reinbold has seen this in Mediterranean specimens of I. wmbilicatum, and the 
same may be seen in J. calodictyon, Decne., from the Canaries. This is also figured by 
Montagne in Webb and Berthelot’s Hist. Nat. des Iles Canaries, ii. part ii. sect. iv. 
(1840) p. 180, tab. 8. figs. 14, le. Curiously enough, Montagne describes the primary 
filaments as dividing into fours (“ venis quinis, mediis erectis, binis inferioribus patenti- 
bus”). Kiitzing also figures the branching of JZ. calodictyon in his ‘Tabulze Phyco- 
logicee,’ vii. (1857) tab. 25, 11. 
Though we have not seen in our specimens the original attachment-disc, we have 
noticed several rhizoids which fasten the thallus to the substratum. They appear to be 
attenuated prolongations of the apex of a branchlet ; sometimes they arise from the side 
of the cell. They are usually dark and partly opaque, and bear a holdfast at the 
extremity (fig. 4). 
SrRuvVEA, Sond. 
5. Struvea Gardineri, sp.n. (Plate 47. fig. 5.) 
S. stipite simplice, rugoso; fronde juniore subelliptico, 5 cm. longo, 3 cm. lato, fronde 
adultiore late expanso, circa 17 cm. longo, 15 cm. lato; reticulo laxo e rhachi 
inconspicua pinnatim ramosa et e ramis ad nodos cruciatim egredientibus iterum 
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