KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 25. N:0 5. 45 



B. A decicled isthraus. 

 (var. /? Wallich, t. VII, f. 12—14). 



4. var. (i triangulare f. produeta, n. f. Long. 25 — 28, lat. 24 — 25, lat. constr. 10, 

 long. isth. 5 — 6 ,«. Wallich, Mscr. Xo. $2, f. 3. 



5. — — — f. tensa, n. f. Long. 26 — 35, lat. 25 — 32, lat. constr. 8 — 10, long. isth. 

 6—8 t*. Wallich, Mscr. Xo. Q2, f. 3 a. 



T. XVIII. 1, f. 7; 2, f. 6; 3, f. 17 a, c; 4, f. 17 1»; 5, f. LO-, 11. 

 Wallich, in Desm. Beng. gives dimensions: 



1. Long. 16—20.5, lat. 20.5—30.5 ,u. 



2. 20.5—26, » 18—30.5 /u. 



3. 4. 20.5—26, » 20.5—30.5 ,«. 



The spherical zvgospores are of a reddish brown colour wheii mature, and are 

 about 17 — 20 /u in diameter. In the 3-anglcd var. thc endochrome is triradiate, each 

 ray bifid, as in Staurastrum commonly. The discovery of the elongated forms sets at 

 rest the question that an isthmus may norraally exist within this genus; cfr De Toni 

 (Sylloge p. 792, definitio generis) isthmis nullis'! Wallichs icons ex Mscr. (copied 

 in part by me) appear to give a suggestion that lateral conjugation may occur, al- 

 though he figures zvgospores in abnorma! positions. Xordstedt, in litt., asks »How 

 can a passage or tube be formed between the apices of two old Desmid-cells?» The 

 question is härd to answer, but, as Desmidian anomalies are of frequent occurrence, 

 I would suggest that if lateral conjugation can and does occur in the Zygnemaceoe it 

 may also take place in the filamentous Desmidiece. 



S. incurvatum, n. sp. Spön. egregium; circ. sexta parte latius quam longum, isthmum 

 distinctum habens; semieellula? ovato-incurvatie, dorso paullo protentae, planae; incisura 

 mediana profunda, sequali, interne rotundata, maxime infra, apertura paullo constricta; 

 membrana glabra. A vertice visum compresso-ovale; a latere clepsydriforme modice 

 constrictum. Conjugatio scaliformis vel lateralis. Zygospora globosa, laevis, mem- 

 brana tenni. 



a. major. Long. 24 — 26, lat. 27 — 30, lat. isth. 7 — 8, crass. 15 — 16 f*. 



b. minor. 16—19, » 24—26, 6, 11 — 13 » 

 T. XVIII, f. 8. Wallich, Mscr. Xo. 67. 



This sp., like the preceding, appears able to conjugate as certain of thc Zygne- 

 macecB both laterallv and with opposed cells of its own or another filament. Dr. Xord- 

 stedt (in litt.) suggests that the spore-like bodies within the cells may be of parasitic 

 origin; this I cannot explain; ncither can I give any explanation of the globular spore- 

 like body shewn by Wallich as being placed bet) c em the apices of two cells, and noted 

 by him. In 67 c Wallich says, »here and therc an empty joint (cellule) having a 

 sporangium at its central //art, in this case påle reddish-green». The only solution of 

 this stränge appearance seems to be that copulating filaments may dissociate after part- 

 completion of union, and that the resulting zvgospores may remain, here and there, 

 attached to one filament. The Zypospore is colourless or påle red; »at a the sporangial 

 cell appears to spring from the junction between two joints, at b from an isthmus be- 

 tween segments.» G. C. W. (Fig 7 is ad nat., the spore only copied from Dr. W.; 



