149 
A. aculeata var. valga Ehrbg. was seen frequently. A. serrulata 
Ehrbg., regarded by Weber (’98) as a variety of A. aculeata, was 
recorded Jan. 24, 1899, and found by Hempel (’99) in December. It 
seems to be rare in our plankton. Forms approaching A. aculeata 
var. brevispina Gosse were also noted, but they, too, are rare, being 
recorded only in February and March, 1899. A. aculeata var. 
curvicornis Ehrbg. was noted April 29, 1896, at 70°. 
Anurea cochlearts Gosse.—Average number, 69,393, distributed 
as follows: <A. cochlearis (sensu strictu) together with A. cochlearts 
var. macracantha Lauterborn, 9,421; A. cochlearts var. tecta Gosse, 
15,432; and forms with posterior spine of intermediate length 
between cochlearts and tecta which include A. cochlearts var. stipttata 
Ehrbg., 44,540. Numerically this is one of our important species, 
containing over one ninth of all the rotifers in 1898. It is surpassed 
only by Brachionus bakert (with varieties included), Polyarthra, and 
Syncheta. Average number of eggs, 32,358. 
This is a perennial planktont, appearing in every month of the 
year throughout the whole range of temperature. Its entire absence 
in August, 1898 (Table I.), is not paralleled in any other year. In 
1897, for example, there is a well-developed pulse of 45,600 on 
August 24. In 1894, 1895, and 1896 there is a midsummer minimum 
of a few weeks’ duration in July, August, or September, but it is 
irregular in its location. 
While the appearance of sexual cycles was not traced by the 
records of males and winter eggs,—a matter of some difficulty and 
uncertainty in preserved plankton material,—the existence of such 
cycles is suggested by the recurrent pulses of occurrence in this 
species (Table I.). It is possible that the species is polycyclic in 
our waters. The pulses in 1898 are well defined, in fact, somewhat 
better than in previous years. The following table gives the num- 
bers in the pulses in the several years and the dates and tempera- 
tures at which the maxima occurred. 
All of the large pulses save those of November and December 
and one at the close of October (Oct. 25, 1898, 28,500) lie at tempera- 
tures above 60°. The vernal pulse of April-May is the largest and 
appears between 60° and 70°, and the amplitude diminishes as the 
period of maximum heat progresses, though in 1898 there was a 
recurrence of larger numbers as temperatures fell. The optimum 
