Fresh-water Entoniostraca of South America. 91 



Biological Observations. — This form de- 

 veloped rather abundantly in 2 of my aquaria, and was 

 watched for rather a long time. In habits it exactly agrees 

 with the other species of the genus, being a true bottom- 

 form, and only rarely leaving the loose mud, through which 

 it forces itself with great dexterity by the aid of its very 

 movable tail. The swimming motion is very slow, and effected 

 at quite an even rate, the body being kept in a horizontal 

 attitude, with the back downwards. When brought under 

 the microscope in a small quantity of water, the animal 

 was often seen to perform the charateristic abrupt twisting 

 of the posterior part of the body, from which the generic 

 name has been derived. Ephippial females and males were 

 found rather plentifully at the close of the season, the former 

 having the upper part of the carapace very dark, almost 

 black. 



Occurrence. — The 2 aquaria in which this form 

 developed, were both prepared with mud from Argentina. 



The following genera, not mentioned in the present 

 paper, are also represented in the fauna of South America: 



Gen. Daphnia^ Müller. 



D. obtusa Kurz, var. latipalpa, Monier. Buenos Ayres. 



D. cavieervix Ekman \ 



_ _,, \ Patagonia. 



D. commutata Ekman J 



Gen. Moilia, Baird. 

 M. Wierzejskii, Richard. Argentina. 



