86 Gr. 0. Sårs. 



larger than the others. Male not very different in external 

 appearance from female, though smaller, and having the 

 rostrum somewhat shorter; caudal part somewhat thicker, 

 with only the lateral rows of denticles present. Body in 

 both sexes very pellucid and almost colourless, upper part 

 of carapace in ephippial females, however, tinged with yel- 

 low. Length of adult female 0.52 mm, of male 0.89 mm. 



Remarks. — There can be no doubt about the iden- 

 tity of the above-described form with that occurring in Eu- 

 rope and first described by Kurz as Alonopsis latissima. I 

 have very carefully compared the South American form with 

 Norwegian specimens, and can find no différence whatever. 



Biological Observations. — This form, which 

 has hitherto been regarded as one of the rarest Cladocera, 

 developed in my aquaria in immense numbers, and was 

 watched during 2 successive seasons. Like most other Lyn- 

 ceidæ, it generally dwells on the bottom in the loose mud, 

 though at times it is also to be seen freely moving- through 

 the water, or attaching itself to the walls of the aquarium. 

 The swimming motion of the animal is rather slow, and is 

 effected at quite an even rate. In order to catch a number of 

 specimens, it was sufficient to take up by the aid of the 

 dipping-tube, a small portion of mud from the bottom of the 

 aquarium, and to place it in a shallow watch-glass, together 

 with some water. After a short time, the specimens were seen 

 swimming out of the mud, and congregating at the lighter 

 side of the watch-glass, where they could easily be picked 

 up for preservation. Generally, on reaching the surface, 

 the specimens at once floated, with one of their valves out 

 of the water, and unable to immerge themselves again. The 

 sculpture of the shell is best seen in such cases, but may 

 also be easily obserable in wholly submerged specimens. In 



