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 diversicornis 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 Anuroza 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., PI. 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 species among 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. 



Synchazta 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; in 1895, 13,071 and 4,730; in 1894, 7,520 and 1,659. The 

 effect of the disturbed hydrograph of 1896 is seen in the smaller 



