PRESENT HISTORY AND DISTRIBUTION 63 



Of these, the Boreal is perhaps the most peculiar, 

 since it extends on the American side from Labrador 

 to Cape Cod, and, crossing the Atlantic, includes the 

 southern shores of Iceland and the west coast of 

 Norway up to the North Cape. 



When, however, it is borne in mind that at no 

 very remote period of the earth's history there was 

 a land barrier shutting the Arctic off from the 

 Atlantic Ocean, it becomes obvious that the fauna 

 that occupied the southern side of that barrier must, 

 on its rupture, have been acted on by the contending 

 currents of cold and warm water thus brought into 

 contact. Hence it has in part been driven to the 

 southward along the American coast by the cold 

 northern waters that flow down past the western side 

 of Iceland, and in part carried far to the north on the 

 eastern side by the warm waters of the Gulf Stream. 



It is impossible without giving long and tedious 

 lists to adequately define the several faunas of these 

 provinces, but it may be generally stated that such 

 genera as — * Margarita, Lacuna, Vehitina, *Trichotro- 

 pis, Buccinum, *Neptunea, Liomesus, *Trophon, *Admete t 

 Beta, *Yoldia, *Modiolaria, *Astarte, Cyprina, My a, 

 Cyrtodaria, and Lyonsia, are examples of the forms 

 met with in colder regions, those marked with an 

 asterisk (*) occurring in both northern and southern 

 hemispheres, while Nerita, Rostellaria, Pterocera, 

 Cyprcea, Septa, Cancellaria, Voluta, Oliva, Marginella, 

 Harpa, Terebra, Conus, Perna, Vulsella, Spondylus, 



