RHODYMENIACE^. 169 



ous, radiating from a central placenta, and attached to the 

 walls of the conceptacle by subsimple threads ; tetraspores 

 cruciate, lodged in the thickened tips of the frond. — Er- 

 THOEA, from the Greek eu, well, and thoros, a seed. 



This genus was formerly combined with Rhodymenia, 

 and has been separated on account of a difference in the 

 arrangement of the spore-threads, which radiate from a 

 central placenta, instead of rising from a basal one, as in 

 that genus. These characters can only be seen by dis- 

 secting a spore- conceptacle under a microscope, and this 

 is not by any means an easy operation to perform on so 

 minute a subject. 



Euthora cristata. The crested Euthora. 



Frond fan-shaped, membranaceous, one to three inches 

 high, divided into numerous segments, which expand up- 

 wards, and are repeatedly subdivided, the secondary seg- 

 ments being alternate, linear, jagged at the tips, and often 

 fringed. Spores in globular conceptacles, which are ar- 

 ranged irregularly along the margin of all the divisions of 

 the frond ; tetraspores cruciate, in the ultimate branchlets. 

 The branches of those plants which bear tetraspores are 

 more slender than those of plants with tubercles. 



This species is very rare, and is only found on our 

 northern shores. It is of a beautiful bright red colour, 

 and varies much in the width and division of the frond. 

 It grows on the stems of Laminaria, in deep water, and 

 is a summer annual. 



Genus LXXIII. RHODOPHYLLIS. 



Frond flat, membranaceous, forkedly cleft, often lobed on 

 the margin, composed of two series of cells ; those of the 



