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find hundreds of specimens, diffe7-ing in sizt^, but possessing 

 absolutely the same characters, but do not find any near relative, 

 and, in such case, we claim to have found a distinct species. 

 The intermediate forms, if such existed, we do not find, and 

 hence, are unable to ascertain from what direction the species 

 came or where it drifted. The development, in a particular direc- 

 tion, may have been arrested by the extinction of the species, and, 

 in such case, the last form would be stamped with unalterable 

 characters. It is common, in the genus Bdiocrinus, to find 

 specimens differing, only, in the number of plates, in one or more 

 of the interradial areas. That is, the specimens will have the same 

 general form and appearance, and the same arm formula, and the 

 same structure, in the lower part of the regular interradial and 

 azygous areas, but, in the superior part of one or more of the 

 areas, there will be one or two more plates in one specimen than 

 in another. In B. argufus, there would be three species, if the 

 variations in the iuterradials above mentioned weie of specific 

 importance, and if we had more specimens we might have more 

 of the same kind of variations. B. glaber would furnish eight or 

 ten species, among the specimens, in our collections, if such 

 variations constituted specific differences. And so we might 

 almost indefinitely increase the species of Bdiocrinus, if such 

 variations are of specific value. It is (juite true, too, that numerous 

 specimens have been collected belonging to some of the species of 

 Bnfocrinus, that have shown no differences in the interradial plates. 

 But that does not prove that other specimens will not show any 

 differences. It is no evidence at all. On the contrary, it is con- 

 sistent with what we know of animal life to suppose that other 

 specimens will show variations, notwithstanding the appaient fixity 

 in form and structure of any number of specimens that we might 

 happen to collect in any particular species. The number that any 

 one may happen to be fortunate enough to see, in any of these 

 fossil species, is like a drop in the ocean when compared with the 

 millions of specimens that must have existed. 



