164 
Brachionus pala var. amphaceros Ehrbg. 
- -  doercas*Gosse 
- tise “forma spinosus Wierz. 
quadratus Rousselet 
urceolaris Ehrbg. 
ie ss var. rubens. Ehrbg. 
D es ‘““ bursartus Barrois and v. Daday 
vartabil1s Hempel 
Brachionus angularis Gosse.—Average number of females, 
57,890; of males, 25; of summer eggs carried, 29,560; of winter 
eggs, 1,223; of male eggs, 54. Of the individuals, 13,973 belong to 
var. bidens and 43,942 to the type; of the eggs, 2,035 belong to the 
variety and 28,802 to the type. 
The combined statistics of the species will be discussed before 
the type and variety receive separate treatment. This species was 
found in every month of the year and throughout the whole range 
of temperatures, but the period of continuous presence and large 
numbers lies definitely between May 1 and November 1 and above 
60°. In fact, in 1898, 98.6 per cent. of all the individuals were found 
between May 31 and October 4 and above 70°. Approximately the 
same conditions are found in previous years save in 1896, when an 
earlier spring (cf. Pl. X. and XII., Pt. I.) is attended by an earlier 
appearance of this species. Temperature seems thus to have a very 
decided effect upon the seasonal distribution of the species, and may 
have something to do with its apparent absence in the cooler waters 
of our Great Lakes and of L. St. Clair, for in spite of all the work 
done upon rotifers in those regions by Jennings it has been found but 
once—by Kellicott (97) ina cove at Sandusky. This identification 
may be questionable, since he says “I at first took it for B. mollis 
Hempel.’ Notops pelagicus, since described by Jennings (00), is 
found in the plankton of Lake Erie, and according to him this 
species is much like B. mollis in its appearance. In any event B. 
angularis is very abundant in our warm waters and practically 
absent in the more northerly waters of Michigan, whose summer 
temperatures are 10°-15° below that of the Illinois River and its 
backwaters. 
Brachionus angularis presents the usual phenomenon of recurrent 
pulses, but in spite of the large numbers they are rather less regular 
