62 



this species are with B. variabilis. It will be noticed that the 

 ray opposite the azygous area has two arms in B. affinis, B. ap- 

 proximatus, B. verneuilianus, B. variabilis and B. cognatus. The 

 different species have respectively twelve, thirteen, fourteen, fifteen 

 and sixteen ambiilacral openings to the vault, but, in all the 

 changes, one of the rays remains the same. Here is the greatest 

 and best defined evolution, through five species, that has ever been 

 found among the palaeozoic crinoids. In B. verneuilianus, the 

 two- armed ray sometimes changes place with the right lateral ray 

 and sometimes with the left lateral ray, otherwise it is always 

 opposite the azygous area. Suppose we were to throw all these 

 species into one, as an illiterate and inexperienced pretender might 

 do, what would be the result? It would simply wipe out all 

 specific characters belonging to Batocrinus; for, if the arm formula, 

 within the calyx, is not of specific importance, there is no specific 

 character found in the genus, and if all these five species can be 

 dumped into one species, all the rest may be made to follow. 

 This is not indicating that these five species are not closely re- 

 lated, for we think they are. They have a wide geographical 

 range, and are represented by numerous specimens, at many lo- 

 calities. What we think is, that here is an evidence of evolution 

 of species, accompanied with varietal changes in each species, 

 which tends to prove that one species arose from another, or 

 might have arisen from another. We have no idea which species 

 came first into existence or from whence it came. It may have 

 been that from the twelve armed species arose all the others, or 

 it may have been that the commencement was from the fourteen- 

 armed species, and, that, by evolution, rays were gained in one 

 direction and lost in another. If the more numerously rayed spe- 

 cies were to be regarded as the more highly developed, it would 

 be taking for granted, as a fact, that which the fossils do not 

 prove and that which we have no right to assume, no matter what 

 emphasis we may place on the number as a test of specific im- 

 portance. We have not used the word Eretmocrinus, for the spe- 

 cies under consideration are true Batocrinus. 



The specimens illustrated are from the Burlington Group, from 

 Burlington, Iowa, and from the collections of A. Albers and S. A. 

 Miller, but others occur in all large collections, for the species is 

 not rare. 



