BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
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and no neritic tropical species having been found. The oceanic forms were rep- 
resented by very few species and small numbers of individuals. One oceanic tropical 
and two oceanic boreal arctic species were found. Marine bottom or semi-bottom 
(tycopelagic) diatoms occurred abundantly. 
17. While the diatom collections and counts were not made daily in any one 
locality, the study of large numbers of surface and deep-water Samples from regions 
widely distributed over the bay indicates that during the years of 1916 and 1920 there 
was a well-marked spring maximum. There are also indications of an autumnal- 
winter increase after a summer minimum, but the diatom counts are ordinarily not 
nearly so high as those of the spring cruises. The diatom counts for the summer 
almost invariably show a marked decrease when compared with those of the spring. 
18. Ordinarily, high diatom counts were found at times of low salinity, but it 
does not follow that low salinity was the cause of the high counts. 
19. Total diatom counts at areas in the mouth of the bay, where the depths are 
shallow and the currents comparatively rapid, were found to be low. 
20. Surface and most deep-water samples of the littoral bottom diatom, Skele- 
tonema costatum, taken during the cruise of October, 1915, show that the largest 
counts were near the mouth of the Potomac River. The vertical distribution of this 
diatom showed the highest counts usually at intermediate depths. The maximal 
counts were found during the spring cruises. 
21. Paralia sulcata, a tychopelagic. diatom with a heavy test, was also found in 
largest numbers near the mouth of the Potomac. The bottom samples as compared 
with surface and intermediate samples contained almost invariably the largest num- 
ers of specimens. The maximal counts occurred during the spring cruises. 
22. The fresh-water protozoan, Difflugia, which is ordinarily a bottom form, 
was found widely distributed over the bay during all the cruises in the year 1916. 
The largest numbers were taken during the July and September cruises. 
23. The silicoflagellate, Didyocha fibula, was caught most abundantly in the 
lower half of the bay. Probably it has an autumnal maximum. 
24. The most abundant peridinian listed by Cunningham for Chesapeake Bay 
was Ceratium furca. 
25. Nodiluca miliaris, one of the cystoflagellates, was found on nearly every 
cruise during 1915 and 1916, but it was only in the lower end of the bay that indi- 
viduals of this species were caught in abundance. 
26. Comparatively few sponges were dredged in the offshores water of Chesa- 
peake Bay. Undoubtedly this scarcity is due largely to the muddy character of the 
bottom and to the lack of solid objects for attachment. 
27. Large quantities of hydroids belonging to the genus Thuiaria have been 
found in Chesapeake Bay throughout the year, although the indications are that they 
are in greater abundance during the spring months. Much of the material collected 
was loose but not floating at the surface. Three species of this genus are represented, 
Thuiaria argentea, T. cupressina, and T. plumulvfera. 
28. The Hydromedusa, Nemopsis bachei, was brought in by the townets in greater 
abundance than any other species in the collections made during 1920 and 1921 (H. B. 
Bigelow). The records indicate that it is present throughout the year. 
29. The jellyfish, Dadylometra quinquecirrha, occurs in large numbers in Chesa- 
peake Bay and is usually in the “Chrysaora stage.” Records for 1915 and 1916 
(Radcliffe) and observations of others support the view that it is abundant in the late 
