283 
m.* save in two instances. Occurrences of small numbers continue 
through July, but from August 1 to October 15 appear the major 
pulses of the year, attaining an amplitude of 1,000 to 8,800 per m.° 
With the decline of temperatures in October, numbers fall to levels 
below 400 per m.’, with one exception (December 14, 1897) at 
700. The percentage of occurrences is, however, high (41 to 44 
per cent.) and declines only to 33 per cent. in January. The period 
of greatest numbers of young thus coincides with that of greatest 
abundance of adults, and lies at temperatures of 70°, and above, in 
channel waters. 
The effect of hydrographic changes upon the occurrence of 
young Diaptomus appears in striking form in the annual averages 
above quoted. In 1898, a year of sudden changes, the average 
per m.* is only 19, while in the stable conditions of the previous year 
it is 560. The July-December production in 1897 is 28 times 
greater than that of 1898. In 1896, a year of recurrent but less 
sudden floods, the average (158) is less than that of 1895 (336), a 
more stable year. The great reduction of adults noted in 1898 and 
1896 is thus paralleled by an even greater reduction of the young. 
Osphranticum labronectum Forbes occurs in the plankton of 
Quiver Lake in small numbers (see Schacht, 98), and was found 
once in channel plankton in June, 1896. 
AMPHIPODA. 
Allorchestes dentata (Sm.) Faxon.—This is an abundant littoral 
species found amid vegetation, especially in the vegetation-rich 
backwaters, such as Quiver Lake. It was not often found in channel 
plankton, being taken only in the summer of 1895, when the July— 
August floods carried away the vegetation which had accumulated 
during the antecedent low water. 
ATROAC TH NDE. 
ACARINA. 
In vegetation-rich backwaters members of the family Hydrach- 
mide were frequently taken, along with other adventitious or- 
ganisms, with the plankton. In channel waters they are less 
frequent, and are represented principally by Atax, which is parasitic 
