6 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



any diatom identities that may exist in the two places is supplied ; 

 for such ships of passage might, and in fact did, bear as freight hosts 

 of marine animal and plant life from one shore to the other. But so 

 far as is known to science there is no communication, bird or other- 

 wise, between Campeche Bay and the Philippines, or even between 

 Campeche Bay and the Pacific coast; and it is certain no drifting log 

 could make such a journey without rounding the Arctic end of North 

 America or the Antarctic end of South America, and thereby subject- 

 ing these subtropical diatoms to the fatal rigors of low temperature. 

 In the matter of diatom transportation, it should also be borne in 

 mind that the difficulties that confront these organisms do not apply 

 to some other marine groups. Thus they must be literally transported 

 from one spot to another, as their limited locomotion consists merely 

 of crawling infinitesimal distances, but not of free swimming; and 

 also the brief life duration of the individual, only a few days at most, 

 prevents its bridging over long-continued adverse conditions during 

 an extensive journey of many thousands of miles. It is pretty sure 

 the Campeche Bay diatoms have not made the trip to the western 

 coast of America by any means whatever, seeing that its character- 

 istic species have never been reported from those regions. 



If we try to see in this Campeche Bay-Philippine diatom parallel 

 a case of "discontinuous distribution" the lateness of the appearance 

 of diatoms geologically, hardly as early as the bottom of the Pliocene, 

 would still leave us confronted by the barrier of the American continent, 

 preventing any transportation to the Pacific Ocean ; while if we imagine 

 an eastern transportation, the western shores of Africa, the Indian 

 Ocean or the shores of Java, Sumatra, or Celebes would be much more 

 likely to afford us Campeche Bay forms than the Philippine Islands, 

 lying so far east of them. There are indeed many species common 

 to the Philippines and these islands of the East Indies, but they are 

 not Campeche Bay diatoms. 



The list of coincidences here given is very incomplete, because it 

 leaves out many species common to both but having little significance, 

 as they are practically cosmopolitan diatoms. And yet if each flora 

 were grouped into a picture and the two compared, these additional 

 forms, not peculiar to the two places but present in both, would greatly 

 increase their resemblance. I think it will be admitted there is a 

 greater significance in the duplication of unique varieties in the two 

 floras than in the duplication of species, because it indicates a peculi- 

 arly close and exact correspondence carried out to its minutest degree. 

 In other words, such cases are not merely similar but literally identical. 

 Thus the slight incurving on the dorsal side of Amphora spectabilsi 

 Gregory which marks the variety figured in Schmidt's Atlas, plate 40, 

 figure 21, from Campeche Bay, is sharply duplicated in my specimen 



