362 ALG.fc CONFERVOIDE^:. [Zygnema. 



70. Zygnema. Ag. Zygnema. 



Filaments articulated, simple, finally united by transverse 

 tubes. Endochrome forming dotted, spiral rings, which, after 

 conjugation, are condensed into a globule in one of the filaments. 



Name, Zyyos, a yoke, and r^u, a thread; aptly expressive of 



the curious conjugation of the filaments. 



1. Z. nitidum, Ag. (shining Zygnema); filaments dark-green 

 parallelly joined, articulations with numerous arching spires. — 

 Ag. Syst. Alg. p. 82. — Conferva princeps, Vauch. — C. nitida, 

 Dillw. Coif. t. 4./. C. (bad), i 



In ditches, not rare. — Filaments dark-green, intensely lubricous, as thick 

 as horse-hair, rigid, forming large masses. Articulations usually a little* 

 longer than broad ; but Capt. Carmichael has found them six times as 

 long as their diameter. After conjugation, the filaments become crisped, 

 fragile, and lose much of their lubricity; the spires are soon after de- 

 ranged and the contents of one articulation discharged through its tube 

 into the opposite one, where they form a dark-coloured globule. The 

 other species undergo similar changes. 



2. Z. deciminum, Ag. (two-spired Zygnema); filaments dark- 

 green parallelly joined, spires double cruciate. — Ag. Syst. Alg. 

 p. 81. — Conferva jvgalis, Dillw. Conf t. 5, and C. nitida, t. 4. 

 /. A. B. 



Ditches, extremely common. — Very variable in the length of the 

 joints. Spires double, crossing each other, like a continual multiplica- 

 tion of the Roman numeral X, whence the specific name. 



3. Z. quininum, Ag. (one-spired Zygnema); filaments pale 

 yellow-green parallelly joined, spires simple. — Ag. Syst. Alg. 

 p. 80 ; also Z. longatum and condensation of the same author. — 



Conferva spiralis, Dillw. Conf. t. 3, and C. longata, Syn. 

 Coif. p. 49. 



Ditches and ponds, very common, forming cloudy pale-green masses. 

 — Filaments marked with a spiral line, resembling a multiplication of the 

 numeral V. 



4. Z. cur vdtum, Ag. (curved Zygnema); filaments green un- 

 branched very slender here and there slightly bent and com- 

 bined by their angles, joints cylindrical four times as long as 

 broad, colouring matter in a triple irregular series of dots. Sm. 

 — Ag. Syst. Alg. p. 79 Conferva stictica, E. Bot. t. 2463. 



Ditches in Henfield level, Sussex, Mr. Borrer. — This species appears 

 to be intermediate between the Genera Mougeotia and Zygnema. 

 " When young, the colour is a dull pale-green, and about 3 imperfectly 

 spiral lines of shining granules are with difficulty distinguishable : after- 

 wards these lines become more conspicuous, the rest of the filaments 

 being now perfectly colourless, and their component granules larger, but 

 their arrangement is still irregular. The threads subsequently unite here 

 and there, not by every joint, and their connecting processes are usually 

 nearer to one end of the joint than to the other. Such filaments are 

 divaricated at the points of connection, rather less abruptly than in Z 

 genufiexa. In some of the combined joints the contents appear un- 



