24 G. O. Sars. 



more or less bright yellow. Length of adult female about 

 2 mm., of male 0.68 mm. 



Remarks. — This form is probably the same as 

 that briefly mentioned by Mr. Richard (1. c.) as a variety 

 of S. serrulatus Koch. The specimens examined by that 

 author were, however, in such a bad state of preservation, 

 that they did not admit of more accurate investigation and 

 comparison. As I have had a very good opportunity of 

 studying this form in the living state, I am enabled to state 

 with full certainty its distinctness from the European species. 

 In additon to its somewhat larger size, it is easily distin- 

 guished by the far less prominent posterior projection of the 

 carapace, and a somewhat different shape of the head. The 

 marginal denticles, moreover, which in 8. serrulatus extend 

 throughout the whole length of the hind edges, are in this 

 species always limited to their uppermost part only, this 

 character, indeed, having given rise to the specific name here 

 proposed. 



Biological Observations. — This handsome form 

 developed very abundantly in several of my aquaria, and 

 was watched for a considerble length of time. In some cases 

 2 distinct sexual periods could be stated in the course of 

 the same season, each period commencing with very prolific 

 parthenogenetic generations, and concluding with the appear- 

 ance of ephippial females and males, the latter often in 

 great abundance. 



In its habits this form closely agrees with the European 

 species, being on the whole a true bottom animal. More 

 generally the specimens are seen quietly attached either to 

 the walls of the aquarium or to some aquatic plant grow- 

 ing on the bottom, the chief means of attachment being 

 apparently the peculiar, hooked apical seta of the upper 



