210 
the species is adventitious in the plankton. The greater part of the 
occurrences were recorded above 50° and the larger numbers above 
60°, indicating an optimum during summer months. The record in 
Table I. refers to the species figured by Jennings (’00) under this 
name. 
Rattulus sulcatus Jennings was found seven times in the plankton 
in July and August during maximum temperatures. It is probably 
adventitious in the plankton. 
Salpina brevispina Ehrbg. was found September 5, 1895, at 
74°, and April 29, 1896, at 70°. 
Salpina eustala Gosse was found July 13, 1894, at 82°. 
Salpina macracantha Gosse was found September 5, 1895, at 74°. 
Salpina ventralis Ehrbg. was found July 29, 1895, at 75°. In 
common with other species of the genus it is adventitious in the 
plankton. 
Schizocerca diversicormis v. Daday.—Average number of females, 
46. The earliest record of this species was June 1, 1896, at 70°; and 
the latest, September 20, 1895, at. 78°. Most of the records and 
the larger numbers are in July-September during the period of 
maximum heat, in which its optimum conditions must be found. 
Egg-bearing females were also found in these months. This species 
is closely related to the Anurea aculeata group, and like it is exceed- 
ingly variable, especially in degree of development of the various 
spines. Variety homoceros Wierz. was found in May, June, and 
August, 1896. Five sixths of all the individuals recorded were 
found in 1896, and the fact that this was a year of unusually dis- 
turbed hydrograph (Pt. I., Pl. X.) suggests that this form may be 
to some extent adventitious in our plankton, but no direct relation 
to the access of flood waters can be traced. 
Lauterborn (’98a) lists this speciesamong the summer planktonts 
of the Rhine, and Seligo (’00) finds it in large numbers, with a maxi- 
mum in July, in lakes near Danzig. Zacharias (’98) reports it in 
German pond plankton, Zimmer (’99) finds it in the Oder, and 
Schorler (’00) in the summer plankton of the Elbe. 
Syncheta pectinata Ehrbg.—Average number of individuals, 
3,950; of eggs, 13,823. It was much more abundant in previous 
years, averaging in 1897 23,227 and 28,230; in 1896, 7,064 and 
7,927; 11895, 13,071 and 4,730; an 1894, 7,520 and) 1-639="5tne 
effect of the disturbed hydrograph of 1896 is seen in the smaller 
