12 G. 0. Sårs. 



the head, and in the much broader inner duplicatures of 

 the valves. In external appearance it more resembles the 

 European species D. brandtianum Fisher; but in neither of 

 the 2 northern species is any trace of the inner duplicatures 

 of the valves, so strongly developed in the present form 

 (see fig. 5), to be found. As to the other anatomical details, 

 the female does not exhibit any perceptible différence from 

 those species. The male, however, differs rather conspicuouly 

 in the far less elongated antennulæ (see figs. 1, 8), and more- 

 over in the much simpler structure of the sexual appendages 

 (see figs 7, 10), the latter being very largely developed and 

 boot-shaped in both European species. The resting ova in 

 this species (see figs. 2, 3) are remarkable for the numerous 

 spiniform processes radiating from the surface, and giving 

 them a scabrous appearance. This peculiar structure has 

 also recently been mentioned by Dr. Daday in African speci- 

 mens of this species. 



Biological Observations. — Numerous spe- 

 cimens of this form developed in my aquaria, and were 

 watched during 2 successive seasons, the residue of the 

 aquaria, at the close of the 1 st season, being kept in a dried 

 state until the next summer, when it was again used for 

 hatching operations. 



In habits, this form exactly agrees with the European 

 species, being a true «plankton-form». In the aquaria it was 

 always found freely suspended in the water, more or less 

 near the surface, the powerful antennæ spread to each side, 

 and only now and then making a vigorous stroke, whereby 

 the body was pulled forwards or upwards. The attitude 

 of the animal, while quietly suspended in the water, was 

 generally a more or less erect one; but on moving, it 

 assumed, as a rule, a more horizontal attitude. 



