Fresh-water Entomostraca of South America. 49 



Remarks. — This is the largest of the hitherto known 

 species of Mona, and, as is well known, is one of the com- 

 monest European forms, having been confounded, however, 

 by some authors with the nearly-allied species, A. quadran- 

 gularis of Müller. I can see no difference between the 

 Brazilian form and the European species ; but for the purpose 

 of close comparison, I give figures of both sexes on the 

 accompanying plate, from specimens reared in my aquaria. 



Occurrence. — Numerous specimens of this form 

 developed in some of my aquaria prepared with mud from 

 Sâo Paulo. That they were in reality raised from the mud, 

 and not, as might perhaps be assumed, accidentally intro- 

 duced among the aquatic plants, is proved by the occurrence 

 of a well-marked specimen in a sample taken by Dr. v. 

 Ihering at the same place from which the mud was derived. 



Distribution. — Besides from Europe and Brazil, 

 this form has been recorded from Siberia, the Azores, Ice- 

 land, Greenland and North America. The Australian form, 

 A. Whiteleggi G. O. Sars, is very nearly related to this 

 species, but is apparently distinct. 



19. Alona Ilieringi, n. sp. 



(PI. XI, figs. 2, a— c). 

 Specific. Characters. — Female. Carapace, 

 seen laterally, oval quadrangular in form, greatest height 

 somewhat in front of the middle, posterior extremity obtusely 

 truncate, with the upper corner sub-obsolete, lower broadly 

 rounded, dorsal margin boldly arched in front, ventral al- 

 most straight. Head somewhat procumbent, with the dorsal 

 margin slightly arched, rostral projection not much produced. 

 Surface of shell quite smooth, without the slightest trace of 



4 — Archiv for Math, og Naturv. B. XXIII. Nr. 3. 

 Trykt den 14. Marts 1901. 



