202 
Noteus quadricornis Ehrbg.—Average number, 19. This is a 
rare species in the plankton, being found in 1895 and 1896 in July at 
maximum temperatures, and in 1898, on April 12, at 52°, and on 
November 8, at 46°. 
Notholca longispina Kell.—This species, which has been found 
in the summer plankton of many European and American waters, 
especially our Great Lakes, was noted but once in the Illinois—in 
January, 1895 (Hempel, ’99). It seems to prefer cooler and purer 
waters. 
Notholca striata Ehrbg.—Average number, 437, including varie- 
ties. This is a winter planktont in our waters, appearing in 1897 on 
November 30, at 34°, reaching a maximum of 10,840 March 22 
(Table I.), at 51°, and disappearing April 19, at 52°. It reappears 
the following autumn on November 1, at 45°, and attains a maxi- 
mum of 4,000 March 21, at 37°. In previous years the occurrences 
all le within the limits of November 1 and April 24 with the excep- 
tion of two records in 1895—September 5 and October 15, at 74° and 
56°. The spring maximum in 1896 (7,778) was on April 10, at 
52°, and in 1897 (4,260) on March 22, at 43°.” In each year ite 
single pulse, that of March—April, is indicated. Minor fluctuations 
during the winter (Table I.) are in some cases attributable to flood 
agencies. 
The temperature limits of this species are quite definitely estab- 
lished. The species reappears in autumn when 45° is reached, and 
declines rapidly in the spring after 50° is passed and is but rarely 
found above 60°. It attains its greatest numbers late in winter or 
early in spring in the face of flood conditions, though the numbers 
attained in the channel waters are never very large. 
Empty loricee have been found in the plankton after the decline 
of the species in April, and females with a single egg were noted in 
small numbers in 1895 during the rise of the pulse. 
I follow the suggestion of Weber (’98) that N. striata should 
include as varieties the following: N. labts Gosse, N. jugosa Gosse, 
and N. acuminata Gosse. Examination of many individuals in the 
plankton proves beyond a doubt the great variability of the organ- 
ism whose seasonal occurrence we have traced. It varies in the 
length of the posterior spine, in the proportions of the lorica, and 
in the development of the striz and the anterior spines. Of a total 
of 81,227 of Notholca striata in this wider sense, 68,887 were referred 
