296 BRITISH SEA-WEEDS. 



in a defined, transparent sheath ; connecting-cells sphe- 

 roidal, slightly flattened. Zoospores large, oblong, about 

 once and a half as long as broad, and twice the diameter of 

 the ordinary cells, generally formed in pairs on each side of 

 the connecting-cell, dark brown when ripe. 



This species was found growing on Cladophora fracta, 

 in a brackish ditch, at Shirehampton. 



Genus CXXX. SPERMOSIRA. 



Threads lying in dark-green, somewhat gelatinous layers, 

 simple, cylindrical, composed of a series of lens-shaped 

 ordinary cells, with larger, compressed, connecting-cells at 

 intervals, each thread enclosed in a transparent, mem- 

 branous tube. Zoospores formed from the ordinary cells. — 

 Spermosira, from the Greek sperma, a seed, and seira, a 

 string. 



The tube which envelopes the thread is the character 

 by which this genus is distinguished from Sphcerozyga. 



Spermosira litorea. The shore Spermosira. 



Frond a dark green, fleecy layer, composed of nearly 

 straight, robust threads ; ordinary cells short, compressed, 

 of a blue-green colour; connecting-cells pale-red. Zoo- 

 spores elliptical, dark brown. 



This species grows on floating plants in muddy, brack- 

 ish ditches. 



Spermosira Harveyana. Dr. Harvey's Spermo- 

 sira. 



Frond a layer of much curved, slender threads ; ordinary 

 cells nearly the length of their diameter ; connecting-cells 

 somewhat square, rather longer than their diameter, which 



