VIl] CORALLINACEAE. 183 



French authors may be definite organic bodies, but it is 

 unwise to attempt to determine their affinities within such 

 narrow limits as have been referred to in the above resume. 

 The structure of the bituminous deposits is worthy of careful 

 study, and it is by no means impossible that further research 

 might lead us to accept the view of the earlier investigators, 

 that the brightly coloured organic-like bodies may be inorganic 

 in origin. 



C. RHODOPHYCEAE. (florideae. red algae.) 



The thallus of the members of this group assumes various 

 forms, and consists of branched cell-filaments of a more or less 

 complex structure. Cells of the thallus contain a red colouring 

 matter in addition to the green chlorophyll. The reproduction 

 is asexual and sexual ; the formation of asexual reproductive 

 cells (tetraspores) in groups of four in sporangia is a character- 

 istic method of reproduction. Sexual reproduction is effected 

 by means of distinct male and female cells. 



With the exception of a few fresh -water genera all the red 

 algae are marine. The Rhodophyceae, like the Cyanophyceae 

 and Chlorophyceae, include a shell-boring form which has been 

 found in the common razor-shell \ Several genera live as 

 endophytes in the tissues of other algae. The recent species 

 of this section of algae are characteristic of temperate and 

 tropical seas. One subdivision of the red algae, the Coral- 

 linaceae, is extremely important from a geological point of view 

 and must be dealt with in some detail. 



CORALLINACEAE. 



The thallus is usually encrusted with carbonate of lime ; it 

 is of a branched cylindrical form in the well-known Corallina 

 officinalis, Linn, of the British coasts, of an encrusting and 

 foliaceous type, in the genus Lithophyllum, and of a more coral- 

 like form in the genus Lithothamnion. The reproductive organs 

 occur in conceptacles, having the form of small depressed 



1 Batters (92). Vide also Schmitz (97) p. 315. 



