270 



AQUATIC MICROSCOPY FOR BEGINNERS. 



7. Chydorus (Fig. 182). 



The surface of this nearly spherical shell is usually 

 reticulated. The beak is long, curved, and pointed, 

 being sharp in the female. The posterior border is 

 truncate in young specimens, becoming more rounded 

 in the old. The eye is present and single. The eggs 

 are hatched in the brood-cavity, as usual. The ani- 

 mal occurs abundantly early in the spring, usually 

 near the bottom where it lives chiefly on vegetable 

 matters. The motion is rolling, and somewhat un- 

 steady and uncertain in appearance. 



8. Alon6psis (Fig. 183). 



The lower or free edge of the shell is fringed with 

 bristles, which are longest in front. The beak is long, 

 pointed, and separated 

 by some distance from 

 the body of the shell. 

 Eye large. One of 

 the feet (the third) 

 has a long spine- 

 fringed with short 

 "hairs on the edges, 

 and often reaching to 

 the posterior margin 

 of the shell. The sur- 

 face is usually marked by a few conspicuous diagonal 

 lines. The animal's movements are slow. 



Fig. 183. — Alon6psis. 



g. SfDA. 



The shell is long and narrow, with the head sepa- 

 rated from the body by a slight depression. The pos- 



