268 
SUPPLEMENT 
believe that, from the degree of temperature necessary to then- 
existence, they abound in the fresh waters of warmer cli- 
mates ; while, on the contrary, they are very rare, if even they 
exist at all, in the very northern regions. 
The local habitations of the Crustacea, considered generally, 
are very various : the most numerous of these animals are 
aquatic and marine, and some few genera, such as oniscus, 
armadillo, &c. are alone truly terrestrial. Certain brachyur- 
ous decapods penetrate very far into the land, but are forced 
to re-enter the sea at the period of coupling and laying. 
Some others, such as thelphusa, though they have forms very 
analogous to those of the marine crabs, do not quit the fresh 
water, and all the entomostraca, except limulus, caligus, and 
some animals approximating to the last, are also inhabitants 
of fresh water only. 
Among the marine species, the majority do not quit the 
shores, while others live in the high seas, and have nothing to 
repose on but those floating banks of sea-weed so abundant 
between the tropics. Moreover, the littoral Crustacea do not 
all sojourn in similar localities: some, as dorippus, and certain 
inachi, reside at depths of from two to four hundred feet, while 
others continually sport on the surface of the waters, and pass 
one half of their existence on the shore, which is continually 
washed by the waves. Many species are met with only in 
rocky situations, abounding in madrepores, and of difficult 
access ; while others seek the bottom of the fine and shifting 
sand, into which they sink themselves. 
Among those which come to land and make a tolerably long- 
sojourn there, many brachyurous Crustacea (the ocypods) 
excavate tolerably deep burrows, at the entrance of which 
they usually remain on guard. Some (the ranini) are said 
even to climb on elevated places, and often to mount on the 
roofs of the Indian cabins 
