70 BRITISH SEA-WEEDS. 



Genus XXIX. RALPSIA. 



Frond leathery, crust-like, composed of jointed, closely 

 packed, vertical threads, spreading in irregular patches over 

 the surface of the rock to which its lower surface is attached. 

 Fructification in warts scattered over the upper side of the 

 frond. — Ealpsia, named in honour of John Ralfs, Esq., a 

 ■well-known botanist, 



Ralfsia verrucosa. Warty Ralfsia. 



Fronds from one to six inches in diameter, of a dark 

 brown colour, marked with concentric lines. 



This very peculiar plant, which is called Ralfsia deusta 

 in the ' Phycologia Britannica,' has more the appearance 

 of a lichen than of a sea-weed. It is common on the 

 shores of the North Atlantic Ocean. 



Genus XXX. ELACHISTA. 



Fronds parasitical, composed of two kinds of jointed 

 threads; the inner, or axial series, forkedly branched, and com- 

 bined into a tubercle ; the outer, or peripheric, not branched, 

 coloured, radiating from the tubercle. Fructification, pear- 

 shaped spores attached to and hidden among the inner 

 threads. — Elachista, from the Greek elachista, the least. 



All the species of this genus are insignificant, and 

 very liable to be overlooked, and in consequence their 

 geographical distribution has not been very accurately 

 determined. Certain of them are known to be com- 

 mon on all the shores of Europe, and on the coast of 

 North America, and they are probably equally abundant 

 in other localities, indeed, wherever the plants on which 

 they are parasitical are found. The beginner will not 

 easily make out the specific characters of these minute 



