ZYGNEMACEE. 93 
Spirogyra turpis, Kutz. Tab. v. t. 19, f. 2. Rab. iii. 238. 
Spirogyra cateneformis, Kutz. Tab. v. t. 19, f. 1. Rab. iii. 
238. Petit Spirogyra t. 3, f. 9-12. 
Rhynchonema abbreviatum, Kutz. Rab. iii. 248. 
We venture to differ from our friend Mons. Petit in uniting four of his 
species. In fact, if four species are to be accepted, we see no logical 
grounds for refusing to accept a dozen, because of the excessive vari- 
ability in the sterile cells. 
Plate XXXVI, fig. 2. a, b, sterile cells X 200; ¢, conjugating cells 
with zygospores X 200; d, fertile cells of Rhynchonema form with zygo- 
spore X 200; e, fertile cells of mirabilis form with zygospores X 200; 
J, conjugating cells of catenwformis form with zygospores x 200 ; g, h, i, k, 
outline zygospores x 400. 
Spirogyra flavescens. (Hass.) Cleve. 
Sterile cells with the ends truncate, 2} to5 times longer than 
broad, chlorophyll bands single. 
Spores attenuated, twice as long as broad, membrane even, 
chestnut colour. - 
Sporiferous cells swollen, and usually longer than the spores. 
Size. Cells:02mm.diam. Zygospore -05 x ‘024 mm. 
Cleve Monog. Zygn. p. 19, t. 3, f. 6, 7. 
Boggy pools on heaths, &c. 
form a. gracilis. 
Zygospore about ‘03 mm. diam. 
Zygnema gracile, Hass. Alg. t. 30, f. 5, 6. 
Spirogyra gracilis, Kutz. Tab. v. t. 18, f.5. Petit Spiro- 
gyra p. 15, t. 3,f. 7, 8. 
Zygnema malleolum, Hass. Alg. t. 34, f. 5. 
Rhynchonema malleolus, Kutz. Tab. v. t. 33, f. 3. 
form b. flavescens. 
Zygospore about ‘02 mm. diam. 
Zygnema flavescens, Hass. Alg. t. 30, f. 9,10. Jenner Fi. 
Tunb. Wells, 180. 
Spirogyra flavescens, Kutz. Tab. v. t. 18,f. 4. Petit Spiro- 
gyra p. 15, t. 3, f. 5, 6. 
Zygnema affine, Hass. Alg. t. 34, f. 6. 
Spirogyra afinis, Petit Spirogyra, p. 18, t. 3, f. 12, 13. 
Rhynchonema affine, Kutz. Tab. v. t. 33, f. 2. 
form ¢. parva. 
Zygospore about ‘01 mm. diam. 
Zygnema parvum, Hass. Alg. t. 80, f,7, 8. Ann. Nat. Hist. 
x. (1842) p.41. Jenner Fl. Tunb. Wells, 180. 
Spirogyra parva, Kutz. Tab. v. t. 18, f. 3. 
This species includes five of Hassall’s species of Zygnema, which sub- 
sequently were relegated by Kutzing, three to Spirogyra and two to 
Rhynchonema, The Zygnema flavescens, parvum, and gracile, are sepa- 
