10 
INDIAN FEESH- WATER FISHES. 
congregation, so that in the majority of cases there is 
little difficulty in deciding the family to which a fish 
belongs. Some species there are certainly which lie 
on the borderland between one family and another, as 
must be expected, but these cases are comparatively 
few. 
Some families inhabit the salt water exclusively ; 
some are confined, as, for instance, the Cyprinidse, to 
fresh waters. Some, as the Salmonidse, are only 
found in the temperate regions of the Northern Hemi- 
sphere, being apparently unable to pass the heated 
waters of the tropics, while others are only found in 
tropical regions, being unable to exist in the colder 
climates. Other families again have representatives in 
all parts of the globe. 
In the fresh waters of India two families are most 
plentifully represented, viz., the Cyprinidse, or carp 
family, and the Siluridse. The latter are easily re- 
cognised by wanting scales. 
The Ophiocephalidse, or Snake-headed fishes, have 
also a good many species in India ; and many other 
families are represented by one or two species, but 
perhaps nine-tenths of the fishes that are usually met 
with belong to one or other of the two first-mentioned 
families. 
(As an example among large animals of what con- 
stitutes a family , we may instance the Family 
Bovidrn, which includes in it, sheep, goats, oxen, 
antelope, bison, etc., each of these forming a separate 
genus .) 
