CRIBRILINID^. 183 



Lepralia of Jolinstou. That the latter is a very hetero- 

 geneous group, and cannot be maintained in its integrity, 

 will probably be admitted by most. There will be less 

 agreement as to the principles on wliich it should be sub- 

 divided, and the constitution of the new genera that are 

 to replace it. Our knowledge of the Polyzoa is not yet 

 sufficient to admit of a strictly natural classification, and 

 our arrangement of them must still be, to a large extent, 

 more or less artificial ; and to some it may appear hardly 

 desirable to interfere with the existing order of things for 

 the sake of a change which, after all, may be merely provi- 

 sional. But it must be borne in mind that, as a matter of 

 convenience, and to facilitate the work of the student, it 

 is essential that the unwieldy collection of forms bearing 

 the name Lepralia should be broken up into groups of 

 some kind or other ; and it seems better to aim at a natural 

 subdivision, even though the attempt should be only par- 

 tially successful, than to perpetuate the purely arbitrary 

 method hitherto in use. 



Of the numerous species ranked under the genus Lepra- 

 lia, many have little in common but general habit ; and 

 to mass them together indiscriminately can only be ac- 

 counted a very rude and provisional kind of classifi- 

 cation. 



I am very sensible of the difficulties — some of them, I 

 fear, insurmountable for the present — which are attendant 

 upon the work of reorganization in this department, even 

 after the valuable labours of Prof. Smitt*. My aim 

 has been to form groups which shall represent the more 

 important variations in the architecture and structural 

 composition of the zooecium. The other principal zooidal 



* See his paper entitled " Bryozoa mai-ina in regionibiis arcticis et 

 borealibiis virentia recensuit F. A. Smitt," CEfv. Kongl. Vctenskaps-Aka- 

 demien's Foi'handlingar, 1867, no. 6, p. 443. 



