THE NAUTILUS. 



A reniform Bivalve, I'/iio margarUifer v. slnualu Lam. 



The parts of the shell and their names are similarly depicted. 

 The questions of species and varieties are 

 then discussed at length. The definition of 

 "species" is good; but that of "variety" 

 seems to us to beg the question entirely. 

 Thus, in one paragraph, a variety is said to 

 be an incipient species ; in another, " varie- 

 ties may be individual, that is, occurring 

 only in a more or less isolated and sporadic 

 way, or they may be a sexual character," 

 etc. American naturalists, at least, do not 

 regard such deviations as this as "varieties," 

 but use that term for what Mr. Taylor calls 

 (Mont.) x -2, showing the " a sub-species, geographic variety or race." 

 nearly straight coluruella. We believe that sexual and " random " 

 Pyriform univalve, Clan- variations should have no place in specific 

 silia lanmata (Mont.). nomenclature. It is also unfortunate that 

 Mr. Taylor (in common with Mine. Paulucci and others) uses the 

 term "mutation '' to express a slighter modification than "variety," 

 as it has a very different significance in palaeontology, expressing 

 the successive stages of a specific form, or genetically related series 

 of specific forms, in successive formations. 



In treating of the causes of form-modification in shells, Mr. Tay- 

 lor states that fluviatile species tend to develop a lengthened shell 

 under the influence of a steady and rapid current, and short forms 

 of otherwise elongated species in lakes and other large bodies of 

 water. 



Section through the shell 

 of Clausilia lauiin<i/<i 



