222 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



latter the type infection is from United States National Museum 

 specimen No. 52144, collected August, 1914, by J. S. Ligon. 



Measurements of an average individual. — Length of body 0.2 mm. ; 

 width of body 0.085 mm. ; thickness of body 0.027 mm. ; length and 

 width of nuclei, first 0.005 mm. by 0.005 mm., second 0.006 mm. by 

 0.003 mm., third 0.007 mm. by 0.0045 mm. ; cilia line interval, anterior 

 0.002 mm. 



This OpaJina shows a general resemblance to Cepeda obovoidea, 

 but is much flatter, is not so pointed behind, and has most of its 

 nuclei ellipsoidal, or perhaps discoid, instead of spheroidal. In my 

 specimens the axial excretory organ is very large. This species is also 

 very similar to many individuals of Opalina obtrigonoidea. 



OPALINAE LATAE. 

 OPALINA RANARUM (Ehrcnberg). 



1 Chaos intestinalis cordiformis Leeuwenhoek (1782). 



"> Flimmerquadrata GozE (1782). 



Bursaria ranartun Ehrenberg (1831). 



Opalina ranarum Pubkinje and Valentin (1835). 



A thoroughgoing study of this common European species would 

 be a valuable thing, studying the marked racial diversity of which 

 there is clear evidence, and following several of the races through 

 their life history with the most careful attention to structural detail. 

 It seems a favorable species for such study because of its accessibility 

 and abundance and its decided diversity. I have not material for 

 such study of this or any other species, and am not delaying the pub- 

 lication of this taxonomic review of the family until I can have ob- 

 tained and have studied such extensive series of infections from all 

 phases of the life history of some species, though without such thor- 

 oughgoing study of one species one's judgment as to single infections 

 or a small group of infections of any species is likely to be erroneous. 

 Without such intensive study one can not properly evaluate the 

 structural characters observed. My material of this Ophalina in- 

 cludes numerous infections from Rana temporaria and one from its 

 variety parvipalmata, as well as infections of somewhat similar 

 Opalinas from other Ranas from the same general region, and I will 

 describe in some detail the conditions found. But this series of in- 

 fections is insufficient for an adequate study. 



The hosts from which Opalina ranarum has been frequently re- 

 ported are Rana temporaria Linnaeus, Bufo hufo (Linnaeus) [Bufo 

 vulgaris Laurenti], and Bufo viridis Laurenti [Bufo variabilis 

 Pallas]. My material includes ranarum-like infections from all 

 these species and from Ra7ia dalmatina Fitzinger. Opalina ranarum 

 is also reported from Bombina bombina (Linnaeus), very unusual: 



