548 AQUATIC PHYCOMYCETES 



Scherffel (loc. cit.) proposed the name Ectochytridium for this genus, 

 as a subgenus of Chytridium, but used the name in a generic sense 

 ("£. willei [Lowenth.] Scherflf."). 



The concept of the genus has been somewhat enlarged to include 

 nonapophysate forms. Salient features are the epibiotic operculate spo- 

 rangia and the epibiotic resting spores which develop after the receptive 

 thallus receives the contents of a small male thallus through a conju- 

 gation tube. It is not unlikely that forms will be found in which this tube 

 is either very short or altogether lacking. If so, the genus as now con- 

 stituted, can well accommodate them. 



KEY TO THE SPECIES OF ZYGORHIZIDIUM 



Sporangium formed solely from the body of the encysted zoospore 

 Sporangium apophysate; on Conjugatae 



Resting-spore wall smooth Z. willei, p. 548 



Resting-spore wall verrucose Z. verrucosum, p. 550 



Sporangium lacking an apophysis; on diatoms 

 Conjugating thalli of like size; on Ankistrodesmus 



Z. parallelosede, p. 550 

 Conjugating thalli of dissimilar size; on diatoms 



Male cell not enlarged, that is, essentially same size as a zoo- 

 spore; resting spore ovate; on Melosira .... Z. melosirae, p. 551 

 Male cell somewhat enlarged ; resting spore subspherical to o\ al ; 



on Synedra Z planktonicum, p. 551 



Sporangium formed from both the cyst and germ tube of the zoospore 



Z. parvum, p. 552 



Zygorhizidium willei Lowenthal 

 Arch. Protistenk., 5: 228, pi. 8, figs. 8-43. 1905 

 (Figs. 4 P-Q. p. 72; 31 R, p. 496) 

 Ectochytridium willei (Lowenthal) Scherffel, Arch. Protistenk., 53: 7, pi. 1, 

 figs. 11-24. 1925. 



Sporangium sessile, single or in groups, spherical, subspherical, or 

 broadly or narrowly pyriform, with a single apical, subapical, or lateral 

 broad operculum (rarely two), wall smooth, stout, colorless, somewhat 

 refractive, not giving a cellulose reaction, typically about 15 [j. in diam- 

 eter, dwarf sporangia 4-5.4 u. in diameter; endobiotic system consisting 

 of a knoblike centrally depressed or irregular structure 1-2 u. in diameter, 



