D.BRYC'E ON A NEW CLASSIFICATION OF THE BDELLOID ROTIFERA. 67 



a whole series of structural developments, and distinguishes the 

 Philodinidae^ not only from the Adinetidae, but from all other 

 members of the class Rotifera. 



The Microdinidae are even more feebly equipped than the 

 Adinetidae. The corona is practically absent, and the animals 

 can only creep about in a slow and clumsy manner by means of 

 the rostrum and foot. They have some little compensation in 

 being able to partly protrude their jaws from the buccal opening. 

 It is hoped that the discovery of forms allied to the single species 

 yet known w^ill provide further indications of its affinities with 

 other Bdelloida, but meanwhile I agree with Murray that 

 M, paradoxa is w^ell placed in a genus and a family of its own. 



The recently discovered and very remarkable species to which 

 De Beauchamp (65) has given the specific name " intermedia " 

 shows a distinct advance in the direction of Microdina in the 

 structure of the mastax, in its adaptation to prehensory move- 

 ments, and in the absence of any throat. But it possesses a fully 

 developed rostrum, and a corona which, although differing in 

 important details from that which is typical of the Philodinida, 

 is nevertheless retractile at will within the mouth, and the species 

 therefore comes well within the limits of that family as indicated 

 in the definition following. 



The family Microdinidae, distinguished by the presence of a 

 rostrum and the absence of a corona, consists therefore of the 

 single genus Microdina, represented by one species. 



The family Adinetidae, having an imperfect or retrograde 

 rostrum, and a corona which cannot be retracted within the 

 mouth, comprises the two genera Adineta and Bradyscela, the 

 latter created to receive the species " clauda,'' which differs very 

 notably from the Adineta type in the structure of the foot. 



The family of the Philodinidae includes all Bdelloids with 

 well-developed rostrum and corona, the latter always capable of 

 retraction within the mouth. With the exception of the four 

 forms placed in the new genera Ceratotrocha, Scepanotrocha, 

 and Abrochtha, the numerous species conform in most respects 

 very closely to one structural plan. 



Of the few deviations from uniformity of plan, I regard as of 

 great importance that which is found in the structure of the 

 stomach of certain species. Although not hitherto employed or 

 suggested as a means of generic distinction, it has nob quite 



