Translated hy Philip H. Nicklin. 115 



I shall cite as examples of this mode of judging, the entirely 

 peculiar system of coloring of the Unio irroratus and cylindriciis ; 

 the unique form of the appendices in the Unio spinosus and in 

 the Symphynota bialata (Lea, 1st volume ;) the peculiar form of 

 the tubercles in the Unio lacrymosns and apiculatus, &.c. 



By combining all these means of exact judgment on the one 

 part, and of logical induction on the other, I am satisfied that 

 we shall recognize in the group of the Naiades, as experience has 

 taught us in others, the truth of that observation, whose expres- 

 sion is recorded in the maxim, Natiira nonfacit saltuni, viz. that 

 exterior unlikeness does not exclude autonomy, and vice versa ; 

 or, iti other words, that two beings inseparably connected by their 

 essential characters, are often much more unlike in their external 

 appearance, than two beings entirely different in essential charac- 

 ters. The demonstration of this proposition is found by the zool- 

 ogist, in the i^aces, so abounding in varieties, of the dog, the ox, 

 the cock, of man himself compared with the reo/ species but little 

 removed, of the quadruraana, the rodentia, the motacillse, the 

 accipitres, etc. The botanist finds it, in comparing the races so 

 prodigiously varied of the pears, the roses, the carnations, of the 

 cereal plants and pot-herbs, with the true species, although differ- 

 ing Imle in appearance, of the genera Ranunculus. Galium, Ar- 

 temisia, Senedo, Carex, Brnmus, etc. The mineralogist and the 

 geologist find it, as every one knows, at every step of their inves- 

 tigations. 



Such, gentlemen, are the principles, upon which, (in default of 

 absolute certainty, perhaps not attainable,) I would reform the de- 

 marcation of the species of the family of the Naiades. And I 

 must say, that no philosopher seems to me at the same time more 

 able, and better situated to accomplish it than Mr. Lea himself. 

 But has the time arrived in which he can thus occupy himself 

 usefully? I thit]k not yet. Possessing the richest of special 

 collections. Mr. Lea has not yet, however, had the opportunity of 

 inspecting all the nominal species. America, where he lives, is 

 evidently the privileged country of the Uniones and AnodontaB, 

 considered with respect to the number of species; but America 

 has not yet been so entirely explored in this point of view, as not 

 to leave a great number of links wanting in that chain, (which 

 should be unbroken if possible,) upon which the reformer should 

 mark his divisions. It would probably be better, still to loose the 



