THE NAUTILUS. 115 



iug fertile only for a generation or two. Crosses of ividely differing 

 forms or races are very fertile, but sterility is the law with members 

 of the same family but of differing species. Has this test been 

 applied to the family Unionidre ? This seems to be the only way 

 the true boundaries of species will be fixed. 



It can be asserted without fear of successful contradiction that the 

 members of this family (Unionidse) are connected in such a manner 

 that it is impossible to draw a limit to any species. The same is 

 true in many other families, recent and fossil, as the Ammonites, 

 snails, sponges, etc. Is it not true that species are mutable, similar 

 conditions and surroundings only yielding like forms ? Dr. New- 

 comb, to settle a dispute, reared from a single pair, five species (?) of 

 Achatinella, their surroundings being varied to produce the desired 

 change. The most cautious recent investigators incline to the theory 

 of mutability of species. The wild dog has descended from the vvolf ; 

 the domestic dog in all its forms from the wild dog ; the domestic 

 cat from the wild cat and the pet guinea-pigs from the wild guinea- 

 pig of Brazil. The domestic forms of these will not pair with 

 ancestors, the new species being evolved by differing conditions. 



Hence it is that almost every branch of Zoology is burdened with 

 synonymy and is in great confusion. The only practical course for 

 the purpose of classification and study of Natural History is to 

 admit that the principal well characterized forms are species. There 

 is no other course open to us and I have concluded from this pro- 

 cess of reasoning that Lea's, Conrad's and others' names, where based 

 on well characterized and differing forms as exhibited in numerous 

 individuals, will have to stand as " good species " in spite of the 

 dictum of individuals. This must be the case or the very founda- 

 tion of all Natural Science will be destroyed and systemization be 

 impossible. It, therefore behooves us to exercise much caution in 

 our strictures upon the work of others especially where we have not 

 the means of knowing the facilities possessed by the one with whom 

 we differ. 



Regarding the classification of the family Unionida^, I think Dr. 

 Lea's Synopsis a pretty close ajjproximation to what we want. By 

 making some changes it becomes a most useful adjunct to the 

 cabinet. It enables the student to hunt down a species by the pro- 

 cess of elimination very expeditiously. I have found some changes 

 and additions expedient. The habitat is entered opposite each 

 species as also a reference to the work, page and plate where it is 



