208 J. MURRAY ON PHILODINA MACROSTYLA, EHR., 



The genus Philodlna I regard as a thoroughly natural one,, 

 although it is generally conceded that the eye-spots are too 

 unstable to serve for generic distinction. Yery closely related 

 species may be found, one of which has eye-spots, while the 

 other has none. The eye-spots, moreover, frequently fail in 

 species which usually have them. I therefore propose to 

 redefine the genus, making Ehrenberg's secondary character 

 the principal one. 



Genus Philodina. 



Toes four. Eyes cervical or none. 



This redefinition makes little change in the perso7inel of 

 the genus — all the species having cervical eye-spots remain 

 in it, with the single exception of P. hexodonta, Bergendal, 

 which is probably the same as P. collaris, Ehr. That species 

 has only three toes, and in other respects its organisation differs 

 profoundly from all other species having dorsal eyes. 



Ehrenberg also defines the genus Rotifer as having " cauda 

 ter furcata," but that is undoubtedly a mistake, as the three 

 species which he at first included in the genus, and all species 

 since discovered which have frontal eyes, also have three toes. 



The new definition causes to be included in the genus a 

 number of species formerly on technical grounds included in 

 Callidina, but which are all of robust frame like the dorsal-eyed 

 species, and agree with them in all essential features. 



The number of those Philodinae unprovided with eye-spots is- 

 not very great as yet, though several have been recently added 

 to the list. The ten known species are P. j^e?i&, P. alphtm,. 

 P. brycei, P. humerosa, P. laticeps, P. 2 )aras ^ ca ) P* kamata T 

 P. spinosa, P. vorax, and P. indica. 



There are some sixteen species known which have eye-spots r 

 making a total of twenty-six admitted species in the genus. 



The genus is not large enough to be unwieldy, yet those 

 twenty-six species are sufficiently diverse, and it is probable 

 that the generic definition is still too wide. 



The species may be arranged in five groups, which are on the 

 whole natural, though one or two species are difficult to place. 



