476 POLYMORPHISM AND LIFE-HISTORY IN THE DESMIDIACEiE, 



Scottish Desm., Pl.ii., f.l3), (i)Cos.Jiavum Roy k Bisset, I.e. Pl.ii., 

 f.l7, and Cos. jyrottiberans Lund. The last three I have not seen, 

 but the others are certain. Cos. jiavum must go wherever Cos. 

 odontopleuTuin goes — the zygospores are exactly alike. The latter 

 has already been placed as a f. minor of Cos. repandum (vide W. 

 ■& G. S. West, Monog. Br. Desm., iii., 54). 



Tlie following variations of this species have been observed 

 here : — 



•Cos. RECTANGULARE var. NODULATUM Playf., «7i<e, 1908, Pl.xii.,f.5 



Long.50-62; lat.38-44; crass.30-r>6; ap.17; isth.lO/x. 



Auburn, Guiklford(23, 45, 60). Cum forma typica. 



This is, as far as I know, the final and fully-developed form. 

 A vagueness about the apex, which seems to belie this, is pro- 

 bably due to the appearance of incrassation at the basal angle 

 and upwards, making the upper part of the cell look weaker by 

 contrast. 



Forma minor. (Pl.xiii., f.5). 



Long.36-38; lat.28-30; ap.14, isth.lO/x, 



Guildford (60). 



Both with and without nodules. This form is almost var. 

 Cambrense (Turn.) W. &' G. S. West, but a little broader. The 

 latter in same gathering. 



&■- 



Var. CAMBRENSE(Turn.) W. & G. S. West, forma. 



Forma semicellulis paullo latioribus; hi/ra tnargmes apicales 

 juxta angulos superiores nodulis singulis utrinque praeditis; 

 lateribus angulisque plus minusve rotundatis. Long. 36; lat.28; 

 ap.14; isth.lO/i. 



Gui]dford(60). 



The nodules in this form were below the apical margin. 



Var. UENTATUM, n.var. (Pl.xiii., f.46). 



Forma semicellulis ad var. nodidatum accedentibus; lateribus 

 6 basi fere parallelis; angulis basalibus dentatis. Long.50-52; 

 lat.38;ap.20-21;isth.8-12/.. 



Guildford(89, 114). 



