424 
VERTEBllATA. 
tempest, and with their dredges and trawling-nets raking the rough bottoms of those rocky coasts, 
and drawing thence turbot, sole, bleak, ray, ling, and a multitude of other uncouth but still coveted 
monsters of the deep— these all follow a profession which not only alfords support to the body, 
but feeds rude spirits with a fierce delight. 
The importance of fishes as a source of national wealth, renders their geographical distribu- 
tion a matter of interest and importance. This seems to be determined by nearly the same laws 
as those which regulate that of other aquatic animals. Climate, composition of the element in 
which they live — whether salt, brackish, or fresh — and conformation of the sea or river-bed, on 
which the depth of water depends, are the chief controlling influences. The leading distinctions of 
form and color between fishes of tropical and those of temperate regions, evhice the influence of 
climate ; the fact of the fisheries for certain species commonly used for food being invariably con- 
ducted in deep water, while others can only be maintained among shallows, shows the influence of 
depth ; the fact pointed out by Sir John Richardson that the seas, marked by ranges of land or 
reefs extending for great distances under the same climatic parallel, are peopled by the same species 
of fishes, is an instance of the action of the combined influences of climate and depth. The dis- 
tinctness as to genera and species of the greater number of river and lake fish from those inhab- 
iting the sea, depends on the second of the three great influences enumerated — that of the com- 
position of the element in which they live. Great depths cut ofi" the range of species even when 
climatic conditions are similar. Hence the fishes of the coast of the United States are for the 
most part distinct from those on the European side of the Atlantic. Some fishes have very 
limited ranges in depth compared with others, and, generally speaking, it may be assimaed that 
those having the greatest vertical range — that is, range in depth — have also the widest horizontal 
extension, a fact depending on the capacity of such species for hving under a greater variety of 
conditions. Barriers of land, as chains of mountains, determining the courses of rivers, are often 
the boundaries between two distinct specific assemblages of fresh-water fish, and in like manner 
a very narrow strip of land may divide two very distinct marine faunas. The distribution of 
marine vegetables, affecting the distribution of numerous marine Tnvertehrata which feed on 
those vegetables, and in their turn serve to furnish food for fishes, will materially afi'ect the dis- 
tribution of many species of the latter. So also will the presence of currents, and even the 
agency of man, assisting often unintentionally in the conveyance of ova from one country to 
another. Distant regions, presenting similar conditions, such as the arctic and antarctic seas, 
are inhabited by species representative yet not identical, and presenting a general aspect very 
similar, depending on characters of form and color, &c. It is probable also that the fishes inhab- 
iting the greater depths of tropical seas resemble those of temperate chmes, and that those of the 
latter in like manner approach arctic forms. 
Considering the immense number of fishes, and the almost endless diversity of their forms and 
their characteristics, it is not surprising that they should present great difiiculties in their classi- 
fication. The arrangement of Cuvier, which we have given in outline in the Introduction to 
this work, was the leading one for a time, but it has been modified by more recent naturalists. 
As we can only give a very brief description of prominent species, we shall notice them under 
five orders, as follows : the Selachia, the Ganoidea, the Teleostea, the Cyclostomata^ and the 
Leptocardia. 
ORDER 1. SELACHIA. 
This order derives its name from the Greek selachos, a shark, and includes the Sharks and 
Hays, and corresponds with the typical species of Cuvier's Chondropterygious fishes. The 
skeleton is entirely of a cartilaginous nature ; the teeth variable, being in the Sharks, which are 
the most active and predacious members of the order, exceedingly sharp, compressed, and occa- 
sionally serrated at the edge ; in the Eays they sometimes exhibit the same trenchant character ; 
in other cases they are arranged in mosaic, and in still others the teeth form broad pavement- 
like plates. They are never inserted into the jaws, but are retained in their position by the 
strong skin of the gums. The fins are variously disposed ; the skin is sometimes quite naked, 
