192 REPORT—1845. 
are too imperfectly known to enable us to ascertain how many of them range 
to the other side of the great ocean. Is there a marked change either in 
generic forms or species between the eastern limits of Polynesia and the 
American coasts ? 
The desultory observations I have thrown out respecting the distribution 
of fish apply more particularly to the marine osseous fish, but those which 
compose the sub-class of Cartilaginei have even a more extensive range. The 
sharks of the China seas and of Australia are for the most part identical. 
One of them, the Cestracion, has attracted the attention of geologists on ac- 
count of the teeth of an ancient species having been found in European de- 
posits, associated with fossil palms and other plants of the warmer regions. 
But whatever inference may be drawn from the character of the plants, no 
great reliance ought to be placed on the teeth of the Cestracion as an indi- 
cation of the temperature when the deposit was made. The Australian 
species, or one differing from it chiefly in colour and little in form, inhabits 
likewise the seas of China and Japan; and when deposits now forming are 
revealed to the eyes of future geologists, its spoils will be found associated 
with the Huon pines of Van Diemen’s Land, the Hucalypti of New Holland, 
the fern trees of New Zealand, or with the vegetation of the temperate parts 
of Asia, according to the locality that is explored. 
With regard to freshwater fish, China agrees closely with the peninsula of 
India in the generic forms, but not in species. It abounds with Cyprinide, 
Ophicephali and Siluride. As in the distribution of marine fish the inter- 
position of a continent stretching from the tropics far into the temperate or 
colder parts of the ocean separates different ichthyological groups; so with 
respect to the freshwater species, the intrusion of arms of the sea running 
far to the northwards, or the interposition of a lofty mountain chain, effects the 
same thing. The freshwater fish of the Cape of Good Hope, and the South 
American ones are different from those of India and China. The remarkable 
mailed Siluroids of intertropical America are unlike any freshwater fish of 
Africa or Asia, while the Ophicephali are almost exclusively Asiatic ; a genus 
of the same family being found at the Cape of Good Hope but none in Ame- 
rica. The Cyprinide have been said to be wanting in Polynesia and Au- 
stralia. In the coral islands of Polynesia their absence is clearly owing to 
the want of lakes or rivers, and of Australia it may be said that the rivers 
have not been sufficiently explored. They exist in the larger islands of the 
Javan chain, and it is likely that the same species will hereafter be detected 
in the northern parts of Australia. And the Cyprinoid family is not alto- 
gether unknown in Australia. A curious marine Cyprinoid, the Rhynchana 
greyi (Ichth. of Voy. of Erebus and Terror), is not rare in the seas of New 
Zealand and South Australia. It has been a prevalent opinion that the Cy- 
prinide are exclusively freshwater fish, but the Catastomz of North America 
frequent the estuaries of the rivers which fall into the Arctic sea, living indif- 
ferently in the salt and fresh water, and thriving wherever they find proper 
food. The anadromous Percoids differ very slightly in form from others that 
are purely inhabitants of fresh waters ; and many examples of the same kind 
might be adduced from among the marine fish *. The common anadromous 
salmon (Salmo salar) does not descend beyond the 41st degree of latitude on 
the eastern coast of America, and it is probably restrained within similar bounds 
on the eastern coast of Asia, for we find no representations of it among the 
* In the genera dmbassis and Apogon, there are species truly marine, with others closely 
resembling them, that inhabit fresh waters and even thermal springs of high temperature. 
Most of the Coregoni pass their whole lives in inland waters, but many individuals, carried 
down to the sea by river floods, live and thrive in the brackish or salt waters of the estuaries : 
and the brackish lagoons of Port Essington on the north coast of Australia furnish full-grown 
examples of Carangi, Mesopriones, and other fish considered to be purely marine. 
