168 MARINE PROVINCES. 



M. d'Orbigny makes the same observation. On the other hand 

 M. Morch, of Copenhagen, says he has received Tellina opercu- 

 lata and Mactra alata from the west coast and also from Brazil ; 

 and M. Deshayes gives the following extraordinary ranges in his 

 ' Catalogue of Veneridae in the British Museum ' : — 



Artemis angulosa, Philippines— Chili. 

 Cytherea umbonella, Red Sea — Brazil. 



" maculata, W. Indies — Philippines, Sandwich. 



" circinata, W. Indies — West coast America. 



In these instances there is doubtless some mistake, either 

 about the locality or the shell. As regards the last, Mr. Carrick 

 Moore has shown that the error has arisen from confounding 

 the Cytherea altemiata of Broderip with G. circinata of Born. 

 M. d'Orbigny collected 628 species on the coast of S. America — 

 180 from the eastern side, and 447 from the Pacific coast, besides 

 the Siphonaria Lessonii which ranges from Valparaiso in Chili 

 to Maldonado on the coast of Uruguay, These shells belong„to 

 110 genera, of which 55 are common to both coasts, while 34 are 

 peculiar to the Pacific, and 21 to the Atlantic side of S. America ; 

 an extraordinary amount of diversity, attributable partly to 

 the different character of the two coasts — the eastern low, 

 sandy or muddy ; the western rocky, with deep water near the 

 shore. 



" The comparison of the shells of Eastern and Western America 

 is of considerable interest to geologists ; for if it is true that 

 any number of living species are common to the Pacific and 

 Atlantic shores, it becomes probable that some portion of the 

 Isthmus of Darien has been submerged si7ice the Eocene Tertiary 

 period. Any opening in this barrier would allow the Equa- 

 torial current to pass through into the Pacific — there would be 

 no more Gulf stream — and the climate of Britain might, from 

 this cause alone, become like that of Newfoundland at the 

 present day. 



" Although geological researches seem to show that not only 

 the Isthmus of Darien, but even the Rocky Mountains, were 

 sufficiently submerged during the Miocene Epoch to allow of 

 the free intermingling of the waters of the Atlantic and Pacific, 

 yet the special temperate molluscan fauna of E. and W. America 

 are very dissimilar. There are no grounds for believing a 

 single species to be identical. There are, however, a large 

 number of species (upwards of 50) living on both sides of the 

 northern portion of the continent, and the majority of these 

 exist in the British seas." 



The molluscan fauna of the Panamic and Carribbean Provinces 

 contain very many species in common; these were, for a long 

 period, distinguished- as "representative" species, but the con- 



