MUTATIONS IN CRUiSTACEA OF THE FAMILY ATYIDxE. 791 



occurrence of the mutation is a normal and constant feature of 

 the species.^ 



Professor Bouvier discusses at length the possible explana- 

 tions of these curious pheuomena. He points out that it is 

 impossible to coutinue to regard Atya bisulcata and Ort- 

 mannia Henshawi, for instance, as distinct and independent 

 species; their constant association and their identity in all 

 characters except those of the chelipeds forbid their separa- 

 tion, and it may be added that Professor Bouvier's proved 

 skill and experience as a carciuologist give special weight to 

 his opinion on this point. He also dismisses, and no doubt 



Text-fig. 4. 



Caridina apioclieles. A', A", First and second chelipeds of 

 the typical Caridina-form. B'. B", First and second chelipeds 

 of the O r t ni a n n i a-f orm (O . E d w a r d s i) . After Bouvier. 



rightly, the suggestion that the phenomena are due to 

 hybridisation; and he concludes that the facts he describes 

 have their closest analogy in the "mutations" of de Vries. 



^ The question whether the genera implicated in these phenomena of 

 mutation are to l)e retained as valid is of secondary importance, and 

 hardly concerns more than the convenience of the systematist. If they 

 are to be retained, however, it would seem that a good case exists for 

 the re-instatement of the name Atyoida in place of Ortmannia. 

 Miss Rathbun displaced Atyoida on the ground that the surviving 

 type-specimens of Randall's Atyoida bisulcata, the type-species of 

 Atyoida, have chelaj of the Atya-type. If, however, 0. Henshawi, 

 the type-species of Ortmannia, is only a form of A. bisulcata, the 

 two genera are synonymous and the older name should be used. 



