484 POLYMORPHISM AND LIFE-HISTORY IN THE DESMIDIACE^, 



Var. SUBRENIFORME, n.var. (Pl.xiii., f.9). 



Forma e var. cyclopeo, angulis lateralibus basalibusque conflu- 

 entibus pr-oducta. Semicellulse subtriangulares; apicibus angustis 

 subtruncatis; angulis basalibus latissime rotundatis; lateribus 

 sursum leniter deplanatis, ad apices rapide convergentibus; api- 

 cibus infra marginem interdura papilla instructis. A vertice 

 ellipticse, utrinque leviter inflatte, polis obtusis. Pyrenoidibus 

 singulis. Endochroma verticaliter divisa. Long. 30-35; lat. 23-30;. 

 crass. 15; ap.8-12; isth,5-6/x. 



Canley Vale( 110), Guild f ord( 1 1 4). 



The basal angles of this form are always broadly rounded,, 

 never sharp as in Cos. nitidulum De Notar., and Cos. galeritum 

 Nord. Var. suhreniforme and var. reniforme are produced from 

 var. cyclopeuvi by repeated division. 



Forma mixta — var. cyclopeum et var. suhreniforme, Long.30; 

 lat. var. cycl 28, var. suhreii.^b; isth.6/x. 



Guildford(114). 



Var. RENIFORME, n.var. (Pl.xiii., f.lOa). 



Forma e. suhreniformi producta, dorso depresso. Semicellulfe 

 depresspe, pajne reniforme.s; dorso leniter arcuato. Membrana 

 minute punctato-scrobiculata. 



Found as yet only as mixed forms : — 



Forma mixta 1. — V&.Y. reniforme et\a.v. suhreniforme. Long^ 

 33; lat. renif. 29, snhrenif. 29, ap. 10; isth.6/n. 

 Fairfield(116). 



Forma mixta 2. — var. reniforme et var. cyclo2:)eum, f. Long.- 

 27; lat. renif. 25, cycl. 23; isth.Syn. 



Guildford(114). 



The latter is practically identical with the mixed form figured 

 by Borge, Alg. v. Schweden, T.2, f.26; the size also is the same. 

 It has already been connected with Cos. rectangulare by W. & G. 

 S. West, Monog., p.56. 



I had at first intended arranging all these variations in three 

 sections or subspecies, viz.: — (!) lower sides parallel, (2) lower 



