214 



the evolution these originate from the two cells firstly cut off 

 from the auxiliary cell. But besides these two larger balls several 

 of variable size are present, these most probably originating from 

 divisions of the cell found in the middle after the division of the 

 auxiliary cell. 



Immediately after the fertilization several filaments begin to 

 grow out from the upper end of the cell which carries the pro- 

 carp. These filaments are branched several times and surround 

 the cystocarp forming in this way a kind of involucrum round 

 it (Figs. 199 and 200). 



Fig. 200. Mesothamnion caribaeum nov. spec. Nearly ripe cystocarp. 



(About 40 : 1). 



If we now seek as to which of the other genera belonging to 

 the Ceramiacese our plant is most closely related it is evident 

 from the description and figures above that, in the vegetative 

 formation of the thallus, it comes very near to Callithamnion. The 

 base of the plant, the ramification of the thallus, the chromato- 

 phores and the habit of the thallus on the whole agree perfectly 

 well with that genus and the distribution of the tetrasporangia, 

 too, is quite the same as that found in Callithamnion. On the 

 other hand, with regard to the antheridial stands and especially 

 the building of the procarp and cystocarp, it differs decidedly 

 from that genus. As to these organs it seems to me that we 



