THE FAMILY OF NAIADES. XI 



Cuvier considered that the fact of the succession and of the constant succession, con- 

 stituted alone the validity of the species. 



Dr. Morton comprised his view of species as "a primordial organic form." 



Neither of these definitions fulfil my own idea of what forms a species. It seems to 

 me that a species must be considered to be a primary established law, stamped with a per- 

 sistent form, pertaining solely to itself, with the power of successively reproducing the same 

 form and none other. 



Blainville, in his Manuel cle MaJacologie, divides the Naiades (his Sub-Mytilacea) into 

 Anodonta and Unio, but thinks that species will be found which will make these to be 

 united. 1 



Sowerby says: "The difficulty of ascertaining to which genus of Lamarckian Naiades 

 certain species belong, arises from the very general similarity of form," &c. ; "in fact, an 

 examination of a sufficient number of species will prove that no dependence can be placed 

 upon the characters by which authors usually attempt to discriminate between these genera, 

 and that the transition from one to another is so gradual in some instances, and so strongly 

 marked in others, that it is not surprising that authors, who, having only met with certain 

 species, and not being aware of such intermediate links, should have considered them as 

 the types of new genera." 3 And further : " We think we have already said enough to 

 prove that, unless it be thought wise to elevate each of the peculiar sorts we have men- 

 tioned, and many more, into distinct genera, it will be positively necessary to unite them 

 altogether under one generic appellation." 



Deshayes, in his edition of Lamarck's Animaux sans Vertebres, says it is impossible to 

 separate the genera of the Naiades. "Nous pourrions prendre pour example celui des 

 genres qui est considere comme l'un des mieux caracteris^s. Le genre Symphynote est 

 fonde sur ce caractere remarkable que les deux valves sont soudees entre elles le long du 

 bord superieur," etc. "Nous concluons que tout ce grand ensemble ne peut et ne doit 

 former qu'un seul genre constituent a lui seul la famille des Nayades." s 



1 See page 540. 



2 Zool. Joxirn., vol. i. 



3 Vol. vi. p. 526. — I shall be excused in taking this opportunity to correct an erroneous impression on the mind 

 of M. Deshayes. He says that I was not able to examine the collection of the Museum of Paris. " Malgre cette 

 imperfection qu'il ne pouvait empeeher, le travail de M. Lea se recommende h 1' attention des naturalistes par ces 

 observations judicieuses, des descriptions exactes," etc. It would be strange, indeed, if, after spending so many 

 years in the study of this family, that I should neglect, while in Paris, to see the collections from which Lamarck 

 made so many descriptions. I was frequently at the Museum, and on one particular occasion, by appointment of 

 MM. Blainville and Ferussac, arranged, in the presence of these and other gentlemen, all the species of the Naiades 

 that were in the Museum, and named them ; and also presented to the Museum about fifteen species which were 

 new to that great national institution. I also did the same thing for Baron Ferussac, having designated every spe- 

 cimen in his cabinet belonging to this family. 



