220 MONOCYSTE^. 



I cannot discover the necessity for the genus Ulothrix. Kiit- 

 zing's definitions of the genera Ulothrix and Sphccroj)lea are as 



follow : — 



Ulothrix — " Trichoma simplex, membranaceum, tener- 

 rimum, flaccidum; cellulse gelinese, tenuissimge, hyalinte, ach- 

 romatic^e, abbreviatae : amylidefe delicatissimte, virides, ple- 

 rumque granuliferte, primo extens^e, dein paulatim in fascias 

 transversales contracta?, tandem in opseospermata quatuor vel 

 plura hologonimica transeuntes." 



Sph^roplea. — " Trichoma parenchymaticum simplex, 

 cellula3 tenuissimge membranacea3, substantia chlorogonomica 

 demum in spermatia transeunte repletje, spermatia primo 

 viridia deinceps miniate fusco : epispermio duplici, exterior! 

 filiformi, internum spiraliter investiente, cuncta in series longi- 

 tudinallter digesta." 



The endochrome in all the species of this genus in the 

 young condition is almost uniform ; subsequently, however, it 

 parcels itself into numerous zoospores in each cell. The 

 same remark applies to all the Algce, which are multiplied by 

 means of zoospores. 



The species described in this genus might with some pro- 

 priety be divided into two subgenera, in the first of which 

 should be placed Lynghya zonata^ L. muralis, L. virescens, L. 

 Thompsoni, and L. copulata, in which the filaments are almost 

 always attached, are of a delicate and fragile nature, of a deep 

 green colour, and delight in pure water ; while in the second, 

 Lynghya Jloccosa, L. punctalis, and L. vermicular is ^ should 

 be ranged, these being distinguished by characters the very 

 reverse of those just enumerated, they being rarely attached, 

 tenacious, of a dull green colour, and inhabitants of impure 

 w^aters. In this division L. prolijica should also find a place. 



1. Lyngbya zonata Hass. 



Plate LIX. Figs. 4, 5, 6 and 1, 2, 3. 



Char. Filaments of considerable diameter. Cells usually 

 rather longer than broad, hut sometimes shorter. Endo- 

 chrome at first quadrangular, not entirely filling the cavity 



