Fresh- water Entomostraca of South America. 35 



and transversely truncated at the tip. Also the manner in 

 which the claw of the 1st pair of legs terminates seems to be 

 very different in the 2 species, the tip in the present species 

 being composed of 3 thin superposed lamellæ (see fig. 8), 

 whereas in that of Prof. Lilljeborg it is only minutely den- 

 ticulate. 



Biological Observations. — This form appeared, 

 in the far greater number of my aquaria, and in some of 

 them multiplied to such an extraordinary extent, as at last 

 to fill up the water with immense shoals of individuals. As 

 is generally the case, the individuals of the first generations 

 that appeared were exceedingly prolific, and propagated ex- 

 clusively in a parthenogenetic manner, the matrix being often 

 found to be greatly distended with numerous ova or embryos, 

 giving the general form of the body an appearance rather 

 different from that in the later generations, in which more 

 generally only 2 ova or embryos occurred simultaneously. 

 In some cases 2 successive sexual periods could be stated 

 to occur during the same season ; but the females of the 

 2nd period did not attain such a large size as those of the 

 1st. The appearance of male specimens was always con- 

 temporary with the first ephippial formation in the females, 

 and their existence seemed always to be of very short 

 duration. 



As to habits, this form, on the whole, agrees with the 

 other known species. It moves rather rapidly in a jumping 

 manner, with the body generally kept in a somewhat prone 

 attitude; and numerous specimens were often seen swim- 

 ming about in the uppermost stratum of the water. At 

 times, however, they were found to keep nearer to the 

 bottom, clinging to the aquatic plants or to the walls of the 

 aquarium. The males, as usual, are still more agile than 



