Assertion: eurypterid | /r/CapableOf | form brackish water fauna
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Source sentences:
text: But let us assume for the sake of argument that the eurypterids and a few other arthropods did form a brackish water fauna; then another assumption is necessary, for, if a class of organisms as a whole, such as the eurypterids, should in any given geological period migrate from the sea to estuaries or other brackish water bodies and at the same time should no longer be able to live in the sea, and should not, on the other hand, become adapted to river water, then the remains of such a class of organisms should be restricted to the geological period in which the migration took place, for the class could not persist unless the estuaries persisted from period to period in the same locality (see objection to this on p. 215 below).