^6 D. BRYCE OX A NEW CLASSIFICATIOX OF THE BDELLOID ROTIFERA. 



1830 there are enumerated nine species, of which one, at least, 

 has not been recognised since. The present arrangement deals 

 with a total of 105 species considered to be capable of recogni- 

 tion, in addition to which some 49 species have been placed in a 

 separate list as either insufficiently described or otherwise invalid. 



These " doubtful " species are not necessarily hopeless. Before 

 the lists are again revised, further observations may well have 

 provided sufficient reason for reinstating some of them among the 

 species considered good. 



I do not desire to offisr any remarks upon the position to be 

 assigned to the Bdelloida among other Botifera. Although it 

 would now seem that the Bdelloida do not stand quite so far 

 from the others as was formerly believed, yet the interval which 

 separates them appears still to be a wide one. It is sufficient to 

 accept the position assigned to them by Plate and Wesenberg 

 Lund and to regard them as an order of the sub-class Digononta, 

 distinguished from the Seisonacea by their ramate jaws, their 

 more or less effective rostrum, the telescopic retractability of 

 their distal segments, and their contractile cloaca. 



To the order of the Bdelloida I assign the three families, 

 Piiilodinidae, Adinetidae, and Microdinidae. In my opinion 

 both Janson and Wesenberg Lund, in i-ejecting the family 

 Adinetadae of Hudson and Gosse, have failed to appreciate the 

 physiological difference, which is so intimately connected with 

 the structural distinctions between the Adinetidae and the 

 Philodinidae. The former family, while possessing certain minor 

 capacities which are not shared with the latter, falls nevertheless 

 far behind in structural development and in functional equipment. 

 It need only be pointed out that the Adinetidae are practically 

 unable to swim and that their locomotive abilities are limited to 

 creeping about by means of their corona, aided by the foot. The 

 Philodinidae, on the other hand, can all swim in a more or less 

 vigorous manner. They can also creep about in leech-like 

 fashion by the alternate use of tlip tip of the rostrum and of the 

 foot. But what in my view is most important, is that this 

 creeping about is not in any degree dependent upon the use of 

 the corona. That delicate organ is for the time hidden away 

 within the mouth and so secured from possible injury. This 

 power of withdrawal of the corona without absolute prejudice to 

 the power of locomotion is associated with and consequent upon 



