181 
October 17, 1894, at 58°. With but two exceptions the species was 
taken only above 70°, and the period of most continuous occurrence 
and largest numbers is near the summer maximum of 80°. The 
optimum is thus near the summer maximum. This species was 
never taken in the plankton in large numbers, the greatest being on 
sept. 14, 1897 (20,000), at 84°. On account of the small numbers 
and somewhat irregular occurrences the phenomenon of recurrent 
pulses is here less apparent than it is in more abundant species. The 
appended table records the best-defined ones. These pulses share in 
the general ploiman pulses in only about 50 per cent. of the cases, 
and the most of them coincide with or follow shortly after the pulses 
of chlorophyll-bearing organisms. 
PULSES OF BRACHIONUS MOLLIS 
Year Date Temp. No. | Date | Temp. No. 
Bes eal alge 6 81° 742 Sc aes 75° 954 
1896....| July 18 79° 1,200 | Aug. 21 | 79° 8,400 
1807.1) July 30 85° 11,600 | Sept. 7 80° 20,000 
SO Smee eA o2 aS Sil 800 |- Sept. 27 Se 4,800 
So far as I am aware this species has not been found in other 
waters than the Illinois River and its adjacent backwaters. Hempel 
(799) reports it as most abundant in the marshy environment of 
Flag Lake. 
Brachionus pala Ehrbg.—Average number, including all varie- 
ties: females, 19,969; eggs, 25,974. The following table gives the 
average number, in the several years, of the varieties here included, 
and it will serve to show their relative frequency. 
This is the most abundant species of the genus in our waters, the 
grand total of all occurrences exceeding 9,000,000. As a whole the 
species was much more abundant in the stable year 1897 (180,998), 
and less abundant, all things considered, in the disturbed conditions 
of 1896 (36,665). Asa whole the type form pala is less abundant 
than amphiceros. It forms but 28 per cent. of the total, as compared 
with 68 per cent. included in the latter variety. Dorcas forms less 
