78 ZYUOPHYCEJ2. 



malum, which, however, is not the Tyndaridea anomala of Ralfs and 

 Hassall, as will be evident hereafter. There does not seem to be even 

 a sufficient difference to justify the maintenance of the different forms 

 as varieties. This is the only British species, as far as at present known, 

 with a scrobiculate zygospore, produced in the channel of conjugation. 

 We have followed De Bary in referring this species to Zygnema instead 

 of to Zygogonium. It is unnecessary in a work of this kind to discuss 

 the reasons which have induced us in this, and similar cases, to adopt 

 such a course. It may be well to caution the student at once that he 

 will only waste time in the endeavour to determine species from the 

 sterile threads. In the present, for instance, he would soon discover 

 how hopeless it is to attempt to discriminate between the vegetative 

 cells of this and some of its allies, without the knowledge also of the 

 method in which the zygospore is formed, and its character when de- 

 veloped. 



Plate XXIX. Jig. 1. a, portion of sterile thread X 400 ; 6, threads 

 in conjugation X 200; c, zygospore X 400. 



Zygnema Ralfsii. (Kutz.) De Bary Conj. p. 77. 



Sterile cells 2-| to 3 (rarely 4) times as long as broad . 



Zygospore compressed ellipsoid, twice as long as broad, 

 produced in the inflated conjunctive canal. Sporoderm even. 



SIZE. Cells -016--017 X '02mm. Zygospore -025 X -015 mm. 



Eabh. Alg. Eur. iii. p. 252. 



Zygogonium Ralfsii, Kutz. Tab. v. t. 11, f. 2. Kirsch. Alg. 

 Schl. p. 127. 



Tyndaridea Ralfsii, Hassall Alg. p. 165, t. 39, fig. 4, 5. 



Ann. Nat. Hist. xii. p. 188, t. 7, f. 20. Jenner Fl. Tunb. 

 Wells, p. 182. 



In pools and streams. 



This is the only other British species of Zygnema in which the zygo- 

 spore is produced in the channel, except the succeeding one, which is at 

 best doubtful. It appears to be uncommon, at least in conjugation. 

 First found by Mr. Ralfs at Penzance. It is still to be obtained in its 

 old habitat, and it appears to have been discovered in France and Ger- 

 many. 



From the brief note of De Bary, he seems to recognise this as a dis- 

 tinct and veritable species of Zygnema, according to his interpretation of 

 that genus. 



Plate XXIX. fg. 2. a, portion of sterile thread X 400; b, threads 

 in conjugation X 400. 



Zygnema parvulum. 



Sterile cells 4 to 6 times as long as broad, zygospore globose, 

 produced in the conjunctive canal. 



SIZE. Cells '02--022 mm. Zygospore about equal. 



Zygogonium parvulum, Kutz. Tab. v. t. 12, f. 4. Kutz. Sp. 

 Alg. p. 447. 



Zygnema ordinarium, Berk. Glean. 1. 12, f. 1. ' Harv. Man. 144. 



In standing pools. 



If the Zygnema ordinarium of Berkeley's " Gleanings " can be re- 

 ferred to Zygnema parmdum, that is, as far as we have ascertained, 



