166 BRITISH SEA-WEEDS. 



has decayed ; spores in short-stalked, spherical concepta- 

 cles; tetraspores closely massed in minute leaves, called 

 sporophylla. 



This species is perennial, and is very widely distri- 

 buted, being found on the Atlantic shores of Europe, 

 in the Baltic Sea, and again in various localities in the 

 Southern hemisphere. It is more or less abundant all 

 round our coasts, and in favourable situations grows to 

 a large size. It is to be found, in deep tide-pools, or on 

 tlie perpendicular sides of rocks just beyond low-water 

 mark. The fronds begin to grow in early spring, and 

 soon attain their full beauty. The best specimens, that 

 is to say, those with perfect leaves and of brightest 

 colour, are to be obtained not later than the end of 

 June; but the spores and tetraspores are only formed 

 in winter. It may appear at first sight an unnatural 

 arrangement to separate this species from the Delesseriae, 

 with which it was formerly associated ; but the difier- 

 ences of the fructification are so important, that it is 

 necessary to remove it, not only to another genus, but 

 to a different Order. 



Genus LXXI. RHODTMETflA. 



Prond flat, membranaceous, forked or hand-shaped, often 

 proliferous from the margin, composed of two series of cells ; 

 those within oblong, those on the surface minute. Spore- 

 threads very numerous, issuing from a basal placenta and 

 forming a simple nucleus in sessile, hemispherical concepta- 

 cles scattered over the frond, and opening at length by a 

 terminal pore ; tetraspores roundish, cruciate or tripartite, 

 either collected in cloud-like patches, or dispersed among 

 the surface-cells of the frond. — Ehodtmenia, from the 

 Grreek rhodeos, rosy, and umeen, a membrane. 



