i894- NOTES AND COMMENTS. 403 



which, here given, is of exaggerated size) is the temporal precursor 

 of the cometary outburst of Leptodesma in the Chemung faunas, and 

 is one of the two species occurring in the Hamihon faunas beneath. 



" I am disposed to believe that whenever this method is practicable 

 it will be found of real usefulness not only to biologists in general, but 

 to the palaeontologist in particular, especially in the determination of 

 specific standards or fundamenta, as suggested by Bather. Its success- 

 ful application implies, fiist of all, abundant data. With that 

 prerequisite provided for, profitable comparisons could be instituted 

 between species of distant faunas supposed to be identical, or which, 

 though perhaps identical, may be masquerading under different 

 names ; and between such species in successive faunas of the same 

 region. As a case in point, the brachiopod species Athyvis or Seminula 

 subtilita Hall would serve ; an abundant and remarkably variable shell 

 from the upper Carboniferous. In the lower Carboniferous limestones 

 occurs an allied form, A . subquadrata, and it has been confidently 

 asserted that neither species passes into the geological horizon of the 

 other. Yet the two are greatly alike and each appears under many 

 variations of outline and contour. Assuming that the two are alike 

 in internal structure, which I believe to be essentially true, a series of 

 composites might determine whether or not the variations of the two 

 so-called species reduce to similar fimdamenta, and if they do I 

 should be inclined to regard this as rational evidence of specific 

 identity. Again, the geological value of this method might be 

 tested in such a case as that recently adduced by Professor 

 Prosser, who argues that an extensive series of rocks in central 

 and eastern New York, which appear to be permeated with Hamilton 

 fossils, are not of the age of the Hamilton group, but represent a 

 later geological stage, and that the fossils have, in a considerable 

 degree, undergone modifications from their typical expression in the 

 true Hamilton fauna. As the quality of these variations is hardly 

 palpable under ordinary circumstances, and has not been satisfactorily 

 expressed in words, it ought to appear in composites based upon 

 sufficient data ; and should there prove to be differences in the 

 fimdamenta of specific variations, from the true Hamilton fauna, and 



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