VOL. XIV 

 1891. 



■] PROCEEDINGS OF THE NATIONAL MUSEUM. 125 



coUectiou, all of which are marine species, require any such hypothesis 

 to account lor their occurrence on both coasts of America. 



As already stated, our studies Inive resulted in the addition of but 

 two species {Htnnidoii schninLi and (fi/mnotkonw/unebris) to the list of 

 those thou^iit to be identical on the two coasts. 



This gives us, then, thirteen hundred and seven species that should 

 properly be taken into account when considerinjij this question, not 

 more than seventy-two of which, or 5.5 per cent., seem to be identical 

 on the two coasts. This is very different from the figures given by 

 Dr. Giinther in his " Stiuly of Fishes." 



Now, if from these seventy-two species admitted to be common to 

 botli coasts, we subtract the sixteen si)ecies of wide distribucion — so 

 wide as to kee[> them from being a factor in this i)roblem — we have 

 left but titty-six species common to the two coasts that bear very closely 

 ui)on the water-way hypothesis. This is less than 4.3 per cent, of the whole 

 number. 



But the evidence obtained from a study of other marine life of that 

 region ])oints to the same conclusion. 



In 1881, Dr. Paul Fisciier discussed this same <|uestion in his Mnnncl 

 (le Conchyliohxjie, i)p. 108, 1(J!>, in a section on the Molluscan Fauna of 

 the l*anamic Province, and reached the same general conclusions. He 

 says: " Les naturalistes americains se sont beaucoup preoccupes des 

 especes de Panama qui paraissent identicjues avec celles des Antilles, 

 ou qui sont representatives. P. Cari)enter estime qu'il eu existe 35. 

 Dans la plupart des cas, I'identit*^ absolue n'a pu etre constatee et on 

 a trouvc (luelques caracteres distinctifs, ce qui n'a rien d'etoimant, 

 puis(iue dans I'hypothesc d'une origine commune, les deux races paci- 

 ti<pie et atlantique sont s<''parees depuis la periode Miocene. Voici une 

 liste <le ces especes representatives ou identiques." Here follows a list 

 of twenty species. "Mais ces formes semblables," he says, "con- 

 stituent une infime miuorite (3 i)er cent.)." 



These facts have a very important bearing upon certain geological 

 questions, particuhirll^'> upon that one concerning the cause of the cold 

 of theCilncial Periodl 



In Dr. G-. Fnedierickv WrightVs recent book, "The Ice Age in North 

 America," eight diftferent theories as to the cause of the cold are dis- 

 cussed: The particular theory which seems to him quite reasonable is 

 that one which attributes the cold as due to a change in elevation of 

 different j)arts of the country, and a depression of the Isthmus of 

 Panama' is one of the most impoi-timt changes that he considers. He 

 says (i». 400) : " Should a i)ortion'of the Gulf Stream be <lriven through 

 a depression across the Isthmus- of Panama into the Pacific, and an 

 equal i)ortion be diverteil from tile Atlantic coast of the United States 

 by an elevation of the sea-bottom between Florida and Cuba, the con- 

 sequences would necessjiriljy^ be incalculably great, so that the mere 

 existence of such a possible cause for great changes in the distribution 



