188 



BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



I'ugosa forms may be broad (leiifjth 0.276 mm., width 0.144 mm.) 

 or narrower (length 0.222 mm., width 0.09G mm.). Nuclear and 

 other conditions fail to differentiate the rugose forms from the sub- 

 species proper. Since in numerous other species there are twistec^ 

 ridged, plicate or crenate individuals, and since the rugose condi- 

 tion and slightly shorter shape are all that distinguish the rugosa 

 forms, it seems best not to recognize the rugose individuals as even 

 a distinct variety, but to treat them rather as a fomui., or possibly 

 as only a condition which may be assumed at times under certain 

 undetermined environmental circumstances. 



O °o 



Fig. 157. — Opalina obtrigonoidea maxima, from Blfo boreas : a and 6 magnified 117 



DIAMETERS ; C, A BIT OF THE BODY MAGNIFIED 460 DIAMETERS. 

 OPALINA OBTRIGONOmEA MAXIMA, new subspecies. 



^^276.— TTnited States National Musemn No. 16538. 



Ho^t. — Bufo horeas Baird and Girard, eight infections from west- 

 ern Canada and Alaska. The type infection is from United States 

 National Museum specimen No. 50915, 72 mm. long, from Haines, 

 Alaska, August 16, 1913, E. P. Walker collector. 



