2 20 FRESH-WATER BIOLOGY 



13(12) Pseudopodia ray-like, . . Amoeba radiosa Ehrenherg 1&30, 



Body spherical, with pseudopodia more or less rigid, not withdrawn 

 and reformed rapidly. Nucleus spherical. Habitat, very common 

 among algae; widely distributed. Size, usually less than loo ^ with 

 pseudopodia extended. 



Fig. 278. Amoeia radidsa. ct, contractile vacuole. X loo. (After Leidy.) 



14(11) Pseudopodia not sharply distinguished from the body. . • IS 



15(20) Contractile vacuole spherical. . . . . .16 



16 (17) Posterior extremity villous. . . Amoeba Umax Dujardin 1841. 



Slug-like, usually moving with the broad end forward. Endo- 



^ plasm filled with brilliant granules. Contractile vacuole usually 



J . iO;,-,'?;^.^S / sing's- Nucleus changeable in form. Habitat ooze of ponds. 



%i — ^^-'o^^l^^^jy Size, large individuals usually less than loo /*. 



Fig. 27g. Amoeba Umax. X 225. (After Penard.) 



17(16) Posterior extremity not villous. . . 19 



18 (19) Surface wrinkled, large size. Amoeba verrucosa Ehrenberg 1838. 



A sluggish species, moving by a slow rolling motion. Pseudo- 

 podia short, broad lobes. Body proper enclosed by a delicate 



membrane. Surface marked by lines crossing each other re- 



- "~ ' suiting in a wrinkled appearance. Habitat sphagnous swamps. 



Large individuals may reach 300 n in length when extended. 



Fig. 280. Amoeba verrucosa . X 100 (After Leidy. ) 



19 (18) Surface not wrinkled, small size. . Amoeba guttula Dujardin 1841. 



^--^^^ Body usually oval in outline, moving with the broad end forward. 



I ^./^ Pseudopodia short, broad lobes produced by sudden expansions of the 



] ^'^/y protoplasm. Nucleus single and one large contractile vacuole. Habitat 



(^jy stagnant water. Size 30 ,1. 



Fig. 281. Amoeba guttula. X 400. (After Penard.) 



20(15) Contractile vacuole not spherical. . . Amoeba striata Vena.TA i^igo. 



Moving rapidly by broad extensions of ectoplasm but not changing 

 form rapidly. Usually from two to four longitudinal lines on the surface. 

 Two contractile vacuoles often present, the anterior one changeable in 

 KjvJ shape. Habitat among algae; not abundant. Size, from 30 to 60 ji. 



Fig. 282. Amoeba striata. X 250. (After Penard.) 



21 (3) With shells . Order Testacea . 22 



22 (103) Pseudopodia thick, finger-like, rarely filiform. 



Family Arcellidae . . 23 



23 (96) Pseudopodia thick, sometimes pointed 24 



24 (35) Shell membranous, more or less flexible. . . 25 



25 (32) Membrane covered with organic or foreign particles 26 



26(29) Shell membrane double. . . . Diplochlamys GreeS. . 27 



27 (28) Hemispherical to cup-shaped, loosely coated with organic and siliceous 

 particles. . . Diplochlamys Jragilis Penard 1909. 



Color gray, spotted with black. Inner membrane very fragile 



but capable of distention. Nuclei usually from 30 to 40. Vacuoles 



numerous. Pseudopodia short and thick. Diameter 70 to 125 ■<. 



. «Vf-S Habitat mosses. Not common. Reported from Ontario by Dr. 



■\"/« Penard. 



Fig. 283. Diplochlamys Jras'lis. X iso. (After Penard.) 



