212 Mr. J. W. Kirkby on the Recurrency 



character is of specific or individual worth. The principle, how- 

 ever, which we follow, in common with most naturalists, is to 

 consider all features of individual value that graduate into other 

 features, and all features of specific value that are not subject to 

 such modification, but which stand out as marked characters in 

 all comparisons with other forms. On this method the identi- 

 fications of the preceding list have been made. Whenever a 

 comparison of a Carboniferous with a Permian form showed that 

 the supposed special characters of one passed, by gradual modi- 

 fication, into those of the other, and that there were no charac- 

 ters of the persistent type but such as were common to both 

 forms, we have thought ourselves warranted in referring them 

 to one species. 



Further, we do not consider want of contemporaneity in 

 fossils compared to be of any importance in determinations of 

 species. Time is not, in our opinion, a circumstance that has 

 anything to do with such decisions. And should two indivi- 

 duals present resemblances which we would consider specific in 

 individuals of the same formation, we attach to them the same 

 value, though they belong to separate formations. In both 

 cases we grant equal importance to similar resemblances and 

 differences. We are aware that this is not the principle that all 

 palaeontologists follow, — at least, that there are still a few who 

 argue that want of contemporaneity is an element in determining 

 species : and Prof. King, I suppose, adopts this method ; for he 

 refers to it in support of his opinion of Spirifera Clannyana being- 

 distinct from Sp. Urii. But we hold, with most palaeontologists, 

 that fossil species must be determined on natural-history merits 

 alone, and not in any degree upon differences in their strati- 

 graphical occurrence or geological age. The fact of specimens 

 belonging to different formations ought to be put aside, and the 

 decision arrived at on the same grounds as it is when the speci- 

 mens are from a single stratum. Palaeontologists who rely on 

 this circumstance in distinguishing species rather remind me of 

 those students of entomology who must first know the country 

 of an insect before they venture to say what it is. The former 

 would, moreover, appear to forget that systems and formations 

 of strata are determined to be such by their species being gene- 

 rally distinct from those of other groups. No geologist would 

 consider a series of strata a system or formation, if its fossils 

 were not in the main peculiar. To contend, therefore, that fos- 

 sils are different because they occur in different formations is to 

 argue in a circle. The formation is first proved to be a forma- 

 tion because its species are principally distinct ; and then the 

 species are proved to be distinct because they occur in a different 

 formation ! 



