80 BRITISH DESMIDIACEJK. 



species of Desmids. There are two zygospores in close apposi- 

 tion, each one being formed by the union of a distinct pair of 

 gametes. The four cells which .take part in the conjugation 

 appear to be produced from one individual by two consecutive 

 vegetative divisions, and prior to conjugation they become 

 enveloped in a copious mucus. 



In the other Desmids in which a double zygospore results 

 from conjugation only two cells are concerned in its forma- 

 tion. 



The outer layers of the wall of the zygospore frequently 

 show signs of splitting off, and for this reason Reinsch 'placed 

 the plant in a genus which he named Scltizospura. 



6. Penium Mooreanum Arch. 

 (PI. VIII, figs. 8-10.) 



Penium Mooreanum Arch. Descript. New Cosm., etc. 1864, p. 24, t. i, 

 f. 34-44 ; Eabenh. Flor. Europ. Algar. Ill, 1868, p. 123 ; Cooke, Brit. 

 Desm. 1886, p. 44, t. 17, f. 6 ; West, Alg. N. Yorks. 1889 ; Alg. W. 

 Ireland, 1892, p. 128 ; West & G. S. West, Alga-fl. Yorks. 1900, p. 46 ; 

 Scliiuiclle Beitr. Alg. Schwarzwald. 1893, p. 88, t. 3, f. 8, 9. 



Cells minute, 1J-1-J times longer than their dia- 

 meter, uncon stricted, ellipsoid with truncately rounded 

 apices ; chloroplasts with four or five longitudinal 

 ridges ; cell-wall smooth. 



Zygospore quadrangular-oblong, compressed, with 

 the lateral margins hollow and the angles markedly 

 mammillate. 



Length 19^; breadth 12'7/u; length of zygospore 

 35-42 iu, breadth 25 /i. 



ENGLAND. Kildwick and Howgill Fells, W. Yorks ! 

 Xear Scarborough and Mickle Fell, X. Yorks. (with 

 zygospores) ! 



WALES. Bethesda and Glyder Fach (at 2,200 ft.), 

 Carnarvonshire ! 



SCOTLAND. Inverness, Aberdeen ! , Kincardine, For- 

 far, Perth (lioij $'Bi.wtt). Dumfries ! Kirkcudbright ! 

 Caithness ! Shetlands ! 



IRELAND. Galway ! Kerry! Dublin (Archer). 

 Down ! 



Geogr. Distribution. Germany. Austria. Switzer- 

 land. Italy. Norway. Lapland. 



