405 



The data concerning elevation were taken in part frorn the United 

 States relief map of the Bloomington quadrangle, and in part from aver- 

 ages of the barometric readings. The bench mark established by the survey 

 on the university campus rendered exact correlation possible. 



The following annoted list of species gives a fairly complete picture of 

 the life in this pond. The list of flagellates and desmids is not exhaustive. 

 The diatoms were not identified because of the inadequacy of accessible 

 literature. However, it may be stated that the diatom flora consists of 

 bottom inhabiting forms. 



RMsopoda — protozoa. 



Difflugia globulosa Dujardin. 



This was the most common protozoan in the pond. It was found at all 

 seasons but was more common in 1910 than in 1909. It is reduced in 

 numbers during the winter but when the temperature begins to rise in the 

 spring, this species begins to increase in numbers. In 1910 this increase 

 was very regular from March to August. The Difflugia in the quantitative 

 plankton collections of that 3^ear belonged for the most part to this species. 

 In these collections the 'number per 100 liters varied from 28 on February 8 

 to 39,780 on August 12. 

 Difflugia oblonga Ehrenberg. 



This variable species was a common form in 1909 but not so plentiful 

 in 1910. 

 Difflugia acuminata Ehrenberg. 



Not common. 

 Difflugia urceolata Carter. 



Common in the winter of 1909-'10. Greatly outnumbered by D. globu- 

 losa in the spring and summer. In plankton material killed in foi'maliu, 

 I found a typical individual of urceolata with the mouth of its shell closely 

 appressed to that of a specimen of D. Globulosa. Whether this was a case 

 of fission, an animal building a new shell or an accident, I am unable to 

 state. I am inclined to the belief that the animal was dividing. Tlie 

 rounded shell was slightly smaller than the spined one. If this be true, 

 the distinction between the two forms is of course not specific. 

 Difflugia corona Wallick. 



Observed occasionally. 

 Difflugia lobastoma Leidy. 



Rare. 



