ENTOHOSTRACA AND PHYLLOPODA. 249 



the head like the trunk of a microscopic elephant. The 



shell is oval, colorless, and the posterior border has a 



spine at its lower angle, never at any 



other point. The net-work of lines on 



the surface may extend over the entire 



shell or be restricted to some one part. 



The eye is large. The eggs are hatched 



in a brood cavity on the back beneath the shell. The 



heart is visible near the centre of the back. Bosmina 



is not so common as Daphnia. 



4. CEKIODAPHNIA. 



The shell is oval, oblong, or somewhat four-sided, and 

 always beautifully, if coarsely and conspicuously, reticu- 

 lated, the meshes being hexagonal and comparatively 

 large. The head is separated from the body by a de- 

 pression in the shell, and just behind the rather small 

 eye -like spot it has a slight elevation. The eye is 

 usually near the rounded lower margin or tip of the 

 beak-like head. The antennae resemble those of Daph- 

 nia, being long, and divided into two three - jointed 

 branches of equal length. The angle or tooth on the 

 upper corner of the posterior border is usually sharp 

 and conspicuous. 



This Entomostracan is abundant in the writer's lo- 

 cality. It is visible to the naked eye, being about one 

 twenty -fifth of an inch long. In the aquarium its 

 movements are almost distinctive. It seems to prefer 

 the centre of the vessel, where it darts upward for a 



