60 G. O. Sars. 



Thus the small denticles occurring at the infero-posteal cor- 

 ners of the valves vary in number from 2 to 5 on each valve, 

 and the number of denticles clothing the caudal part is al- 

 so rather variable. On the accompanying plate I give figures 

 both of the female and of the hitherto unknown male, from 

 Brazilian specimens. 



Biological Observations. — This form de- 

 veloped in great abundance in several of my aquaria, and 

 was observed for rather a Jong time. In spite of their small 

 size, the specimens were easily recognizable even with the 

 naked eye, by their dark brownish hue and their peculiar 

 jerky movements. In females carrying resting ova (one 

 such ovum only, as usual, was found in each individual), 

 the upper part of the carapace often assumed a very dark, 

 almost black colour. 



Occurrence. — The aquaria in which this form 

 appeared, were prepared with mud from 3 different localities, 

 viz., Sao Paulo, Itatiba and Argentina. The specimens ex- 

 amined by Mr. Richard, and referred to his species Mona 

 Mülleri, were taken by Mr. C. O. Poppe at Lunache, Chili. 



Distribution. — Besides from Australia and South 

 America, this form has also been recorded by Mr. E. Daday 

 from Ceylon. 



28. Alonella diaphaiia (King). 



(PI. X, figs. 3, a-b). 

 Alonella diaphaua (King), G. O. Sars, 1. c, p. 47, PI. ö, figs. 5—7. 

 Syn. Alona Davidi, Kichard. 



Remarks. — This form together with the preceding 

 one, was described and figured by the present author, from 

 some few female specimens raised from Australian mud; and 



