220 MONOCYSTKffi. 



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

 zing's definitions of the genera Ulothrix and Sphavoplea are as 

 follow : 



ULOTHRIX " Trichoma simplex, membranaceum, tener- 

 rimum, flaccidum; cellulae gelineae, tenuissimae, hyalinae, ach- 

 romaticae, abbreviatae: amylideae delicatissimae, virides, ple- 

 rumque granuliferae, primo extensae, dein paulatim in fascias 

 transversales contractae, tandem in opseospermata quatuor vel 

 plura hologonimica transeuntes." 



SPHJEROPLEA. " Trichoma parenchymaticum simplex, 

 cellulae tenuissimas membranaceae, substantia chlorogonomica 

 demum in spermatia transeunte repletae, spermatia primo 

 viridia deinceps miniate fusco : epispermio duplici, exteriori 

 filiformi, internum spiraliter investiente, cuncta in series longi- 

 tudinaliter 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 Lyngbya zonata, L. muralis, L. virescens, L. 

 Thompson!, 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, 

 Lyngbya fioccosa, L. punctalis, and L. vermicularis, 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 

 waters. In this division L.prolifica 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, but sometimes shorter. Endo- 

 chrome at first quadrangular, not entirely filling the cavity 



