Udotex 235 



Habelliform ' fronds,' having a felt-like structure and attached below by 

 rhizoidal branches (Murray & Boodle, '89). In this genus the branching is 

 dichotomous, and the branches, which are invariably constricted at the base, 

 are either cylindrical or moniliforra, with thin walls. In Avrainvillea the 

 filaments have no lateral branches, whereas in Flabellaria there are numerous 

 lobulate lateral branchlets which usually interlock so as to form a close 

 cortex over the expanded frond. 



Callipsygma is but little more advanced, possessing a flabelliform frond 

 with a complanate two-edged stalk. The filaments composing the stalk are 

 approximately parallel, but those forming the expanded frond are not all in 

 one plane as they frequently overlap and are partly superposed (A. & E. S. 

 Gepp, '04; 11). In Cladocephalus (fig. 152) the branches of the coenocyte 

 are more irregular, forming an excentric infundibuliform thallus in which the 

 subparallel medullary filaments are covered by a labyrinthine cortex com- 

 posed of short, densely subdivided ' pseudo-lateral ' branches. 



Zoogonidangia occur in Avrainvillea as terminal expansions on filaments 

 exserted from the flabellum. 



The genera are : Chlorodesmis Bailey & Harvey, 1858 [inclus. Rhytosiphon Brand, 

 1911]; Avrainvillea Decaisne, 1842; Rhipiliopsis A. & E. S. Gepp, 1911 ; Flabdlaria 

 Lamouroux, 1813 ; Rhipilia Kiitzing, 1858, emend. A. & E. S. Gepp, 1911 ; Cladocephalus 

 Howe, 1905; Rhipidodesmis A. & E. S. Gepp, 1911 ; Callipsygma J. G. Agardh, 1887; 

 Boodleopsis A. & E. S. Gepp, 1911. 



Of the above genera, Boodleopsis is unique and its affinities most obscure. B. siplion- 

 acea, the only known species, is a small Alga from the E. Indies forming dense flattened 

 cushions growing on a muddy substratum. Its chief character lies in the abundant 

 ramification of its branches and in the nature of the branching. 



Sub-family UDOTE.E. This sub-family contains five genera in all of 

 which the thallus is calcified. The most primitive forms are certain species 

 of Penicillits, although Udotea javensis is very little further advanced. The 

 genus Udotea is of exceptional interest in view of the phylogenetic series 

 exhibited by its various species, all of which may be traced back to 

 U. javensis. Its stalked fronds are generally flabellate as in Avrainvillea, 

 but are always encrusted with calcium carbonate. The calcareous matter is 

 deposited in the outer gelatinous layers of the wall, but also penetrates into 

 the inner cellulose wall. The calcium carbonate consists of either aragonite 

 or calcite, but is never quite pure, being mixed with varying quantities of 

 magnesium carbonate or calcium oxalate. The degree of calcification 

 depends to some extent upon the species and also upon the insolation to 

 which a given plant is exposed. There are two kinds of calcification: (1) the 

 filaments composing the thallus are each enclosed in a porose calcareous 

 sheath, and are either quite free (as in the capitulum of Penicillus}, or 

 laterally cemented side by side into monostromatic flabella (as in Udotea 



