LAGENIDIALES 929 



incrassata is considered a natural parasite of Saprolegnia .... The host range 

 of Olpidiopsis luxurious appears to be confined to a single species, Ap/iano- 

 myces laevis. 



KEY TO THE SPECIES OF OLPIDIOPSIS l 



In the hyphae of fresh-water Phycomycetes 



Parasitic in Saprolegnia; resting spore predominantly spherical 



Resting spore spiny . , . O. saprolegniae var. saprolegniae, p. 930 



Resting spore smooth O. saprolegniae var. levis, p. 933 



Parasitic in other Phycomycetes ; resting spore spherical or ellipsoidal 

 Parasitic in Achlya and Isoachlya; resting spore predominantly 

 spherical, wall either spiny, tuberculate, fibrillar, undulate, or 

 smooth 

 Companion cell smooth-walled 



Resting-spore wall smooth O. braziliensis, p. 933 



Resting-spore wall variously ornamented 



Resting-spore wall spiny; companion cell always present 



O. fusiformis, p. 934 

 Resting-spore wall spiny, tuberculate, fibrillar, or undulate; 



companion cell present or absent O. achlyae, p. 935 



Companion cell spiny 

 Spines short 



Spines tenuous, the outer wall not continuous with that of 



the resting spore O. index, p. 936 



Spines coarse, the outer wall continuous in most cases with 



that of the resting spore O. various, p. 937 



Spines very long and rodlike O. spinosa, p. 937 



Parasitic in Achlya (and Saprolegnia?); resting spores predomi- 

 nantly ellipsoidal, the walls tuberculate or undulate, never 



spiny O. incrassata, p. 938 



(O. major, p. 940) 

 (O. vexans, p. 940) 

 Parasitic in Aphanomyces ; resting spore spiny 



Resting spore with a smooth-walled companion cell; in A. loevis 



O. luxurious, p. 941 

 Resting spore lacking a companion cell; not confined to A. 



laevis O. aphanomycis, p. 942 



Parasitic in Pythium 



Resting spore without companion cell 



Resting spore predominantly spherical, the yellowish wall 



covered with long tenuous spines O. gracile, p. 943 



1 Note that the key is not strictly dichotomous. 



