72 G. O. Sars. 



moderate size, slightly narrowed distally, upper basal corner 

 rather thick, supra-anal projection considerably produced, 

 lower corner very slight, marginal denticles about as in the 

 preceding species, caudal claws with 2 distinct denticles at 

 the base. Male exhibiting the usual secondary sexual 

 characters: caudal part with a deep incision dorsally above 

 the middle, distal section straight, gradually narrowed, mar- 

 ginal denticles very slight. Colour of female bright yellow, 

 changing to reddish orange. Length of adult female 0.28 mm. 



Remarks. — Both in size and general appearance, 

 this form looks very like C. sphœricus, and also has a simi- 

 lar sculpturing of the shell. On a closer examination, how- 

 ever, several well-marked differences are in reality found to 

 exist, proving it to be a well-defined species. For instance, 

 the form of the lip-plate is very different, and that of the 

 caudal part is also somewhat dissimilar. Moreover, the pecu- 

 liar velvet-like coating of the dorsal face, constantly found 

 in female specimens of the «summer-generatious», is very 

 characteristic. This character becomes effaced only in ephip- 

 pial females by the transformation that has taken place in 

 the upper part of the carapace, sometimes causing a rather 

 conspicuous deformation of the shell. Finally, in the male 

 the caudal part exhibits a rather different form from that 

 in C. sphœricus. 



Biological Observations. — This form was 

 found in great abundance in several of my aquaria, and was 

 observed during- 2 successive seasons. The movements of the ani- 

 mal, as compared with those of C. sphœricus, are unusually slow, 

 though effected in the usual revolving manner. The specimens 

 were often seen clinging to the walls of the aquarium or to 

 the aquatic plants growing on the bottom ; but it was a rather 

 rare event to see them freely swimming through the water. 



