241] /. A. Gardner 43 



also serves as an effective barrier to most of the northern 

 forms. At Chincoteague, Bartsch and Henderson found that 

 while along the ocean side of Chincoteague Island the 

 fauna was consistently northern in its affinities, in the pro- 

 tected inner bight there was an overlap of the southern 

 faunas. Twenty-eight of the 70 species which they have listed 

 are present in the Yorktown fauna and the number of com- 

 mon forms will doubtless be greatly increased with further 

 investigations. The ensemble of the fossil and Eecent faunas 

 is conspicuously similar although the southern element is 

 a little stronger in the former. However, much the same 

 conditions of sandy shores and muddy bogs more or less 

 choked with algal growth obtained in the Yorktown as along 

 the Virginia coast today. The fauna, like those that precede 

 and those that follow it, is characteristically shallow water 

 and it is doubtful if any of the indigenous species lived at 

 a depth of more than 25 fathoms. 



The Duplin fauna is less homogeneous. Mingled with the 

 large pleurotomid element and a considerable number of 

 volutoids, one of the most uniformly deep-water families, 

 are nine species of Ilyanassa, a group that is known to occur 

 only along inter-tidal beaches. The sediments of the Duplin 

 are, for the most part, coarse sands. It seems on the whole 

 reasonable to suppose that the native Duplin fauna lived near 

 the mouth of some rather large estuary and that the streams 

 entering the bay brought down in considerable numbers the 

 beach-dwellers from farther up shore, while strong currents 

 from the south sweeping along the mouth of the estuary 

 contributed not only a southern element of living forms but 

 also a large number of dead shells referrable to extra-limital 

 species. One hundred and thirteen Duplin species are either 

 identical with the Recent forms or so closely allied that they 

 have been confused in the synonymies. Of this number 97, 

 approximately 85%, occur between Hatteras and Florida. Of 

 the remaining 18 only a single species, the rather uncommon 

 Polynices heros, does not range as far south as Hatteras. 

 Most of the characteristic Florida elements, however, are 



