CHYTRIDIALES 491 



Sporangium very broadly obpyriform, nearly as broad 

 as long, extramatrical stalk rigid, prolonged into 

 the base of the sporangium as a plug; rhizoids 



coarse C. surirellae, p. 501 



Sporangium more narrowly obpyriform, nearly twice 

 as long as broad, extramatrical stalk rigid; rhi- 

 zoids delicate C. versatile, p. 501 



Sporangium without a knoblike base, gradually taper- 

 ing basally, sessile; on algae or microscopic animals 

 Operculum very broad; on living rhizopods 



C. lecythii, p. 503 

 Operculum less than diameter of sporangium; on 



Vaucheria C. pyriforme, p. 503 



Sporangium pestle-shaped, sessile or with a short, tenuous, 



extramatrical stalk; on Tribonema C. lagenula, p. 504 



Sporangium cylindrical C. cocconeidis, p. 505 



Rhizoids, where known, unbranched, isodiametric 

 Sporangium wall smooth 



Sporangium sessile, wall of uniform thickness; on diatoms 

 Sporangium narrowly to broadly obpyriform, procumbent 



C. appressum, p. 505 

 Sporangium narrowly ovoid to pyriform ... C. melosirae, p. 506 

 Sporangium borne on a short epibiotic stalk, strongly arched, 

 basal part thick-walled and sterile; on Stigeoclonium 



C. curvatum, p. 506 

 Sporangium wall ornamented 



Sporangium with an apiculus or nodular protuberance on 

 upper part 

 Sporangium with an apiculus; operculum subapical; on 



Epithemia C. epithemiae, p. 507 



Sporangium with a small subapical nodular protuberance; 



operculum apical; on other diatoms . . C. nodulosum, p. 507 

 Sporangium bearing long setae or short conical spines; on 



green algae or pollen C. chaetophilum, p. 508 



Rhizoids arising from a well-defined endobiotic subsporangial 

 swelling (apophysis) 

 Sporangium with one or two apical teeth or spines 



Sporangium with two opposed solid apical teeth; rhizoids broad, 

 isodiametric, arising from opposite sides of a transversely 



fusiform apophysis; on Tribonema C. confervae, p. 509 



Sporangium with a single apical spine surmounting the oper- 

 culum; rhizoids delicate, tapering, arising from the basal 

 region of the apophysis; on Oedogonium . C. mucronatum, p. 512 



