6 



tiiious expansion, with marginal lol)eR. This, type naturally 

 leads up to that of Coclium bursa. Turn., where the thallus 

 is globular, but fixed to the substratum by an extended 

 base, the centre of the mass being filled with a loose net- 

 work of filaments. The third series is represented by the 

 species dealt with in the present Memoir, viz., Codium 

 tomentosum, Stackh. In this series the thallus is cylin- 

 drical and elongated, and branched more or less dichoto- 

 mously. Finally, Agardh establishes a series based on 

 the species Codium elongatum, C. Ag., w4iere the branches 

 are flabellate. 



The nrajority of the species of Codium are included in 

 the third series, and these are bj^ Agardh sub-divided 

 again into two sections, dependent on the form of the 

 lateral branches of the hyphfe, which form the superficial 

 palisade layer. These lateral branches, named "utricles " 

 by Agardh, are, according to him, either {a) smooth and 

 rounded at their apices, or (b) furnished with an apical 

 umbo or point. Under the former Agardh includes C. 

 tomeutosuin. A careful examination of the palisade layer 

 of that species will show, however, that this distinction 

 cannot be rigidly maintained, for some of the palisade pro- 

 cesses are smooth, whilst others are distinctly mucronate 

 (see PI. I., fig. 3j. 



bjuough has now been said to indicate the taxonomic 

 position of the species under consideration, and to define 

 its general relationship to other Chlorophyceffi. 



Distribution. 



Codium tomentosum, the oldest known species of the 

 genus, is widely distributed in the marine waters of the 

 globe. Jf we accept Agardh's view, the species is a native 

 ol' the shores of; the yVtlantic Ocean. On the west it 

 occurs especially on the short^s of bloiida and the Antilles, 



