RHIZOPODA 15 



SUBORDER 1. AMCEBIDA. 



Rhizopoda having lobose pseudopodia which may be finger-shaped or 

 pointed, but are usually not reticulate; shell of chitin or silica usually 

 present, to which sand or other foreign bodies may be attached : 3 families. 



Key to the families of Amoebida: 



a x Naked Amcebida 1. AMCEBIDAE 



a 2 Amoebida with a shell. 

 &! Shell membranous, often with sand and other foreign bodies imbedded in 



it 2. ABCELLIDAE 



& 2 Shell composed of regular plates of silica or chitin ; pseudopodia sharp and 

 often branching and sometimes slightly anastomosing .... 3. EUGLYPHIDAE 



FAMILY 1. AMCEBIDAE. 



Shell-less Rhizopoda, whose pseudopodia are not reticulate; body 

 without definite form and under ordinary conditions constantly changing 

 its shape by throwing out pseudopodia, although covered by a cuticula of 

 greater or less delicacy: about 19 genera, with numerous species in both 

 fresh and salt water. 



Key to the genera of Amoebidae here described : 



0,1 Nucleus absent 1. PROTAMCEBA 



a 2 Nucleus present and usually distinct. 



& x Numerous nuclei, vacuoles, and retractile bodies present 2. PELOMYXA 



6 2 Numerous nuclei, vacuoles, and retractile bodies not present. 



c x Pseudopodia membrane-like, ectosarc reddish 3. PLAKOPUS 



c 2 Pseudopodia not membrane-like. 

 d : Pseudopodia more or less lobose, sometimes slender and spine-like. 



e t Animals not parasitic 4. AMCEBA 



e 2 Animals parasitic 5. ENTAMCEBA 



d 2 Pseudopodia very long, radiating spine-like from body. 



6. DACTYLOSPH^EBIUM 



1. PROTAMCEBA Haeckel. Minute forms without nucleus or con- 

 tractile vacuole, in constant motion, with short pseudopodia: 4 species; 

 in salt and fresh water. 



P. primitiva Haeckel. In fresh and salt water. 



2. PELOMYXA Greeff. Very large forms constantly flowing by 

 means of short pseudopodia; body with numerous nuclei, vacuoles and 

 hyaline rods ; diameter up to 2 mm. : 4 species ; in fresh water. 



P. palustris Greeff. Without projections at hinder end. 



P. villosa Leidy. Possesses numerous posterior projections; about 

 1 mm. in length; body dark and opaque. 



P. carolinensis H. V. Wilson. No rods present, but numerous 

 minute crystals; 1 mm. in diameter. 



3. PLAKOPUS F. E. Schulze. Body changes slowly in form and with 

 pointed pseudopodia which are often joined together by a broad mem- 

 brane: 2 species; in fresh water. 



