328 
BULLETIN OF THE BUREAU OF FISHERIES 
large numbers of individuals were found on every cruise, and they were widely dis- 
tributed over the bay. The counts obtained during the June, July, and September 
cruises were in general the highest, while on the spring cruises, March and April, the 
lowest numbers were found. In other words, the data point to a summer maximum 
following the spring diatom maximum. A marked tendency for the highest numbers 
to be at or near the surface may be seen from the data, a condition which was found 
by Apstein (1906) in the North Sea. (See Steuer, 1910.) 
The data do not show that the highest counts were found usually in the neighbor- 
hood of the mouth of the Potomac River, although such was the case especially dur- 
ing the July and September cruises. 
Many specimens belonging to the genus Prorocentrum (two forms of P. micans 
according to Cunningham) were collected during the 1915 and 1916 cruises. By far 
the largest numbers were found at the time of the summer and fall cruises, and the 
smallest during the midwinter and spring cruises. At area J the surface counts were 
these: October (year 1915), 1,560; December, 320; January (year 1916), 360; March 
40; April, 200; June, 480; July, 8,440; September, 4,200. At 27 meters the counts 
at the same area were: October, 448; December, 120; January, 120; March, no 
count; April, 280; June, 120; July, no count; September, 4,480. The numbers 
found in the surface samples during the cruises of July and September were highest 
in the region of the mouth of the Potomac River, but during other months this relation 
did not hold. In fact the two largest counts taken in the bay were 15,320 at area R 
in October and 92,800 at area X in June — both surface samples collected far north- 
ward in the bay. The time of occurrence of the maximum counts for this genus and 
for other Dinoflagellata mentioned above supports Kofoid’s suggestion (1921) that 
the increase in numbers may be related to the decay of phytoplankton, but it is also 
true that the increase in number took place when the temperature was highest and 
the light strongest. 
Noctiluca miliaris Surivay, a protozoan belonging to the group Cystoflagellata 
was found on nearly every cruise in 1915 and 1916. This form, according to Osten- 
feld’s r6sum6 (1913), occurs only in coastal waters, not in the open ocean and not in 
water of too low salinity like that of the Baltic Sea. Bigelow (1926) has not taken it 
in the Gulf of Maine, and Fish (1925) did not report it from Woods Hole. Its de- 
cidedly irregular distribution in Chesapeake Bay bears out the statement of Osten- 
weeks, and disappear then, while a short distance away they never become numerous. 
A few specimens of Noctiluca made their way north as far as area X in Chesapeake 
Bay during 1915 and 1916, but it was only in the lower end of the bay that they oc- 
curred in considerable numbers. The data show the highest numbers at the surface 
and the largest count (2,400) was that in a surface sample taken at area F during 
September, 1916. While the distribution in the bay was quite irregular, the data 
point to a maximum in the fall with considerable numbers in the spring and early 
summer. During the cruises of January and March almost no specimens were re- 
corded, while during the cruise of July the numbers were low. No conclusion can be 
reached as to the distribution with reference to the mouth of the Potomac River ex- 
cept that the outstanding high counts were not there but in the region of the mouth 
of the bay. 
A rather large number of genera belonging to the Infusoria were represented in 
the plankton samples, and they have been listed and the numbers tabulated by 
Cunningham in the paper of Wolfe and Cunningham (1926). Of these only one 
