32 G. O. SARS. M.-N. Kl. 



ovicclls shining through tiic valves. In spirit-specimcns the colour rapidly 

 changes to a rather uniform bluish green. 



Observations. This large and prett}^ species developed in consider- 

 able abundance in some of niy aquaria, and was succesfullv domesticated 

 during several successive seasons. In habits it agrees with the other 

 species, being enabled to swim rather quickly through the water by the 

 aid of its long natatory setae. More frequently it is, however, found creeping 

 slowly on the bottom, or along the plants growing in the same, at times 

 also ascending the walls of the aquarium in search of food. Only female 

 specimens occurred, and I am therefore much inclined to believe, that it, 

 like most other species of this genus, is exclusely parthenogenetical. 



12. Cypris trigona, G. O. Sars, n. sp. 

 (PI. 5, fig. 3 a— c.) 



Specific Characters. Shell less tumid than in the preceding species 

 and also less densely hairy : — seen laterally, of a pronouncedh' triangular 

 form, with the greatest height in the middle, dorsal margin boldly curved, 

 being almost angularly bent in the middle, and sloping rather steeply to 

 each extremity, ventral margin slightly sinuated in the middle, the sinus 

 being defined in front by a slight expansion, anterior and posterior extre- 

 mities nearly equal, both being obliquely rounded: — seen from above, 

 regularly oval, the greatest width not attaining the height and occuring in 

 the middle, anterior extremity niore pointed than the posterior. Valves 

 nearly perfectly equal, each with a well-defined semilunar marginal area 

 both anteriorly and posteriorly, that of the anterior extremity being 

 particularly broad, and surmounted by a narrow hyaline rim; inner dupli- 

 catures rather large. Surface of shell smooth. Caudal claws comparatively 

 smaller than in the preceding species, but of a similar narrow linear 

 form. Colour light greenish, clouded dorsally with irregular darker shadows. 

 Length of adult female 1,75 mm. 



Remarks. The present species is nearly allied to the preceding one, 

 though easily distinguishable by the less tumid shell, and its pronouncedly 

 triangular form, as well as by the somewhat different colour. 



Description of the female. 



The length of fully adult specimens measures 1,75 mm., and is ac- 

 cordingly somewhat inferior to that of the preceding species. 



