INTRODUCTION. CXIX 



agrees with the skilfully devised system which we owe 

 to Mr. Busk, and which has obtaiued so wide a cur- 

 rency*. As an artificial arrangement, which alone it 

 claims to be, the latter leaves little to be desired, and 

 has rendered the most important service in promoting 

 the accurate knowledge of Polyzoau forms. But, from 

 its very nature, however good of its kind, it could only 

 hold a provisional place. Marshalling the known forms 

 in convenient groups distinguished by easily recognizable 

 characters, it is an admirable instrument in the hands of 

 the student for the identification of species ; but it gives 

 him no clue to their natural relations. Its families are, 

 for the most part, founded on characters of the slightest 

 significance ; and the forms ranked under them have often 

 little to unite them but some trivial peculiarity. Thus 

 the extensive group of the Escharida is based on the 

 ramose condition of the zoarium (a structural feature 

 of comparatively little moment), and includes a hetero- 

 geneous collection of species, many of which have little 

 in common but their branching stem, and are isolated 

 from their nearest of kin ; and the same criticism applies 

 to the genera. 



D'Orbigny's elaborate classification in his ' Paleon- 

 tologie ' t lias one good feature at least : his family 

 groups have a wider range, and embrace diversities in 

 the mode of growth. His genera, on the other hand, are 

 often founded on utterly trivial features, and have been 

 multiplied indefinitely to represent every insignificant 

 variation of habit. As a svstematist we owe him little 



* Britisli-Museum Catalogue, 3 parts ; ' Crag Polyzoa,' PalaBontogra- 

 phical Society. 



t Pal. fran(;aise, Terrains Cret. vol. v. 



