58 



THE GEOLOGIST. 



The Australian and Tasmanian carboniferous rocks hare also 

 afforded then quota of common species, for although, the forms from 

 those continents have not been sufficiently examined, still from a 

 passing glance I have given to collections sent home from Bundaba, 

 and Port Stephen in Australia, as well as from Van Diemen's land, 

 I have already been able to recognize T. hastata, Sp. striata, Sp. 

 glabra, S. lineata, Eh. pleurodon, Street, crenistria, Orthis Michelini, 

 Prod, cora, etc. If again and by a rapid stride we should find ourselves 

 cast on some of the Spitzbergian frozen coasts, we may there 

 pick up several of om 1 common species, such as Sp. OGtoplicata, Strept. 

 crenistria, Pro. semireticulatus, P. costatus, etc., along with other forms 

 not known in Britain, and lastly, not to extend the limits of this paper 

 beyond reasonable bounds, should we visit the prodigiously extended 

 carboniferous regions of America, we shall there also find a vast per- 

 centage of species identical with our own, but which in many instances 

 are still hiding their true characters under the disguise of borrowed 

 names. Possessing as I do a very extensive series of Ameri- 

 can Carboniferous species, and for which I am indebted to the 

 kindness of Mr. Worthen, as well as to that of some other American 

 geologists, and having compared these with our British species and 

 specimens, I may mention from among others not yet sufficiently 

 studied, the following few as being identical with our own S. 

 saccidus, Atliyris ambigua, A. subtilita, A. plano-sulcata, A. lamellosa, 

 A. Eoyssii, Eetzia radialis, Spirifera striata, S. bisidcata, S. lineata, 

 8. TJrii, S. octoplicata, EJi.pleurodon, Orthis MicMlini, Strept. crenistria, 

 Prod, cora, P. punctatus, P. longispinus, P. semireticulatus, P. scahri- 

 culus, P. costatus, Crania quadrata, Piscina, nitida, Lingida mytiloides, 

 etc. 



This rapid but convincing proof of the existence and distribution 

 of many characteristic British species all over the world where con- 

 temporaneous carboniferous rocks have been deposited, should inculcate 

 upon us the absolute necessity of carefully examining and re-examining 

 our species, so as to avoid the unfortunate results that may ensue 

 from arbitrarily narrowing their limits of variation — thus violating 

 the law of nature, as well as retarding the advance of science.* 



Much indeed may be expected from the rising generation of young 

 naturalists, who, unprejudiced and unfettered, may work out for 

 themselves a new path ; and by seeking to determine with more 

 attention than has hitherto been done what are the resemblances that 

 exist between so-termed species, maybe able to trace and connect 

 those modifications that have been produced by time and circumstances 



* Darwin considers the term species as one arbitrarily given, for the sake of 

 convenience, to a set of individuals closely resembling each other ; and it does not 

 effectually differ from the term variety, which is given to its less distinct and 

 more fluctuating forms : that the term variety, again, in comparison with mere 

 differential differences is also applied arbitrarily, and for convenience sake : that 

 no one can draw any clear distinction between individual differences and slight 

 varieties, or between individual differences or more plainly marked varieties, or 

 sub-species or species. 



