RHODOPHYCEA, OR FLORIDEA 235 
very rarely two or three small, round spores in series, 
and they escape through the apical opening of the 
stalked fruit. The tetraspores are very frequently 
formed in stichidia. The family is a large one 
consisting of a considerable number of genera of 
conspicuous size and beauty of form, and some 
of the genera, such as Polysiphonia, Laurencia, and 
Dasya, are rich in species. Plewrostichidiwm, from 
New Zealand, is however an exception, being a 
minute epiphyte of quite different habit from the 
other genera, but of essentially similar structure. 
The Geographical Distribution is world wide in the 
sea; some of the genera, such as Polysiphonia, have 
a range as wide as that of the family. The British 
genera, Bostrychia, Rhedomela, Odonthalia, Lawrencia, 
Halopithys, Chondria, Polysiphonia, Pterosiphonia, 
and Dasya, are for the most part very common on 
our shores. 
Ceranritec. 
This is one of the largest and most widely distri- 
buted families of Red Seaweeds, and members of 
it are everywhere common on coasts where Algal 
life is found at all. The thallus consists of single 
branched cell-filaments, sometimes with a cortex 
formed of rhizoid filaments (not a true cellular cor- 
tex). This false cortex is produced in the genera 
allied to Callithamnion by the outgrowth of rhizoid 
filaments from the basal cell of lateral branches, 
while in Ceramiwm and its immediate allies, such 
filaments spring from the upper ends (Fig. 78, a) 
of the cells of the thallus, forming a peripheral 
