114 AQUATIC MICROSCOPY FOR BEGINNERS. 



out a cause, although in such cases a careful examina- 

 tion of the narrow or stem end of the pear will show 

 long, fine, and colorless pseudopodia issuing from the 

 mouth, and he will know it to be a Rhizopod. After 

 he has recognized a living shell he will have no trouble 

 thereafter in knowing a dead one, and by referring to 

 the following Key he will be able to learn its name, 

 unless it is a member of a very uncommon genus. 



Key to Genera of Rhizopods. 



1. Body without a shell (a). 



2. Body with a shell (i). 



a. Without fine, hair-like rays; pseudopodia thick 

 and blunt (^). 



a. With fine, hair-like rays (in the addition to pseu- 



dopodia) on all parts of the body (c). 



b. Body colorless, very changeable in shape; often 



large. Amxba, i. 



c. Body orange in color or brick-red, with short pin- 



like rays. Vampyre'lla', 2. 



c. Body colorless or greenisTi {d). 



d. Rays, not the pseudopodia, rigid, forked at the 



ends; body often green. Acanthocystis, 3. 



d. Rays flexible, not forked. Actindphrys, 4, or 



ActinosphcBrium, 5. 



e. Shell a latticed globe on a long stem. Clathru- 



h'na, 12. 

 e. Shell formed apparently of sand-grains (/). 

 e. Shell not formed of sand-grains (^). 

 /. Not inclined ; pear-shaped ; or globular with spines 



at the summit. Diffliigia, 6. 

 /. Inclined; circular or oblong, thicker and with 



spines at the rear. Centropyxis, 7. 



