It has been found more convenient to take as northern boundaries the narrowest part of the straits near the Arctic circle, Bering Strait on the Pacific side, and on the Atlantic side the narrowest part of Davis Strait, and of Denmark Strait, then the shortest line from Iceland to the Faeroes, thence to the most northerly island of the Shetlands and thence to Cape Statland in Norway.
The north to south distance from Bering Strait to the Antarctic circle is 9300 m., and the Pacific attains its greatest breadth, 10,000 m., at the equator.
The Cossack Simon Dezhneff is thought to have made a voyage, in the summer of 1648, from the river Kolyma, through Bering Strait (which was rediscovered by Vitus Bering in 1728) to Anadyr.
Shelving gradually upward from the low flats of Siberia the general continental level rises to a great central waterparting, or divide, which stretches from the Black Sea through the Elburz and the Hindu Kush to the Tian-shan mountains in the Pamir region, and hence to Bering Strait on the extreme north-east.
Bologninus Zalterius on a map of 1566, and Mercator on his famous chart of 1569, separates the two continents by a narrow strait which they call Streto de Anian, thus anticipating the discovery of Bering Strait by more than a hundred and fifty years.
The earliest names associated with the exploration of Bering Strait are those of Russians seeking to extend their trading facilities.
The present family doubtless originated in the northern half of the Old World, whence .it effected an entrance by way of the Bering Strait route into North America, where it has always been but poorly represented in the matter of genera and species.
The boundary between the two powers, as laid down by the treaty for purchase, was a line drawn from the middle of Bering Strait south-west to a point midway between the Aleutian and Komandorski Islands dividing Bering Sea into two parts, of which the larger was on the American side of this line.