Note 103 — Chapter XVII · BARRIERS TO DISPERSION OF RIVER FISHES

There are three species of darters (Cottogaster copelandi Jordan, Hadropterus evides Jordan and Copeland, Hadropterus scierus Swain) which are now known only from the Ozark region or beyond and from the uplands of Indiana, not yet having been found at any point between Indiana and Missouri. These constitute perhaps isolated colonies, now separated from the parent stock in Arkansas by the prairie districts of Illinois, a region at present uninhabitable for these fishes. But the non-occurrence of these species over the intervening areas needs confirmation, as do most similar cases of anomalous distribution.