BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
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bottom were 28.30 per mille, 10.9° C., and 18.93 per mille, 2.7° C., respectively. Also 
specimens of Balanoglossus have been reported from areas S and X farther up the 
bay. Balanoglossus undoubtedly occurs in abundance on the sand flats in the south- 
ern part of the bay. 
UROCHORDATA 
The dredging records show that the ascidian, Molgula manhattensis (DeKay), 
was widely distributed over the northern half of the bay. It was taken in largest 
numbers in the region between the Patapsco River and Kent Island. Only a very 
few specimens were found below the mouth of the Potomac River, and none, so far as 
our records show, below the mouth of the Rappahannock River. 
CEPHALOCHORDATA 
No specimens of Amphioxus have been discovered in our dredgings, but Branchi- 
ostovna virginix Hubbs (formerly known as B. lanceolatus ) has been found on several 
occasions by collectors. See Rice (1880), Hubbs (1922), and Hildebrand and 
Schroeder (1928). 
VERTEBRATA 
The only vertebrates collected on our cruises were fishes; and these have been 
reported in another publication by Hildebrand and Schroeder (1928), together with 
an extensive collection made by them both inshore and in deep water. 
CONCLUSIONS 
The conclusions arrived at below are based on data resulting from frequent 
ecological investigations of some thirty areas widely distributed over the offshore 
waters of Chesapeake Bay. These investigations have been undertaken, usually, 
during all seasons, often over a period of two or three years and in a quite uniform 
manner. 
1. Chesapeake Bay is a shallow, tidal, slow-moving body of water, averaging, 
in offshore regions, from 9 to 12 meters (30 to 40 feet) in depth. Water of oceanic 
salinity (35 per mille) does not enter the bay but large volumes of fresh water are 
emptied into it by many rivers. 
2. A deep-water channel, which lies for the most part nearer the eastern shore of 
the bay, shows, at intervals, deep-water holes, some of which attain a depth of a little 
over 47 meters (156 feet). 
3. The bottom is largely muddy with few rocky areas; but along the shores, 
especially in the southern part of the bay, there are sandy regions. 
4. While Chesapeake Bay is a tidal body of water, the currents are weak; and 
there are, ordinarily, no extensive replacements of fresh water by sea water and vice 
versa during flood tide and ebb tide, respectively. It follows that salinity samples 
collected from one end of the bay, to the other during a period of four or five days 
afford a fairly good idea of the salinity conditions for the whole bay during that time. 
5. On the other hand, there are regions, such as at the mouths of rivers, at the 
head of the bay, and at the mouth of the bay, where the salinity may change rather 
rapidly, especially during periods of river freshets, unusually high tides, and long- 
continued wind from one direction. Furthermore, the study of deep-water currents 
shows that, during the autumn and winter, the deep water at times may move con- 
tinuously, although slowly, into the bay during periods which are considerably longer 
than those of the ordinary flood tide. 
