CODIUM. 329 
coasts, but only two of these, V. dichotoma, Lyngb., var. 
marina, C. Ag., and V. thureti, Woron., have been 
definitely identified in the L.M.B.C. area. 
TV. VALONIACEZ. 
The thallus in this order retains its primitive cellular 
form or is branched, but shows no differentiation into axis 
and appendages. ‘The sporangia are formed directly from 
portions of the vegetative thallus. 
One genus only occurs in the British Algal Flora, viz., 
Halicystis, included by Wille (loc. cit.) under Valonia. 
Hf. ovalis was first discovered by Murray and Schmitz in 
Loch Goil, in the Clyde Sea Area, in 1892, but later it was 
found by Robertson at Lamlash, Arran (vide Phycological 
Memoirs, Pt. I1., and Journal of Bot., vol. XXXII, p. 
345). 
V. CoDIACEZ. 
The Codiaceze include 8 genera, Viz. : Chlorodesmis, 
Penicillus, Aurainvillea, Rhipocephalis, Callipsygma, 
Udotea, Halimeda, and Codium. The last named alone 
occurs in English waters. 
The thallus of the Codiaceew is of varied form and 
organisation ; some genera, e.g., Halimeda, being incrusted 
with calcium carbonate. The filaments of which the 
thallus is composed are profusely branched, and the 
branches are closely interwoven and bound together in 
such a manner as to form almost a definite tissue. 
Generally speaking, the filaments so woven together 
form a medullary region from which arise short swollen 
branches, standing at right angles to the long axis of 
the thallus, and forming a superficial limiting layer, 
the so-called ‘‘palisade layer” or “tissue.” From the 
sides of these ‘‘palisade cells’’ arise the sporangia or 
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