228 



FRESH-WATER BIOLOGY 



99 (98) Small size; foreign elements small. 



Phryganella hemisphaerica Penard 1890. 



Shell hemispherical, composed of small diatom shells 

 and sand grains. Pseudopodia usually slender, some- 

 times thick. Found in the ooze of ponds and lakes. 

 Diameter 40 to 55 M- 



FIG. 321. Phryganella hemisphaerica. X 250. (After Penard.) 



100 (97) Shell chitinous, without or sparsely covered with foreign ele- 



ments 101 



101 (102) Shell occasionally with foreign elements attached. Aperture ter- 



minal Cryptodifflugia Penard. 



Representative species. . . Cryptodifflugia oviformis Penard 1890. 



This species has a transparent, yellowish or brownish shell without foreign 

 elements attached. Ovoid in form. The protoplasm does not fill the shell and 

 pseudopodia are seldom extended. Found in marshes. Length 16 to 20 /*. 



FIG. 3 2 2. Cryptodifflugia oviformis. X 450. (After Penard.) 



FIG. 323. Platoum panum 

 X 725. (After Penard.) 



102 (101) Shell without foreign elements. Aperture terminal or sub terminal. 



Platoum F. E. Schultze. 



In 1875 Schultze described a form under the name Platoum parvum. 

 Ovoid with smooth envelop without structure, slightly elastic, aper- 

 ture terminal or subterminal. Penard, more recently, observed 

 numerous empty shells and inactive organisms which he provision- 

 ally refers to this genus. Some had undulating envelopes with 

 apertures terminal or directed obliquely. Nucleus and contractile 

 vacuole each single. Pseudopodia not observed. Length 16 to 21/1. 



In preserved material from Alaska, G. H. Wailes found forms 

 which he considers within this genus, probably P. parvum. Thus 

 far this is the only record of the genus in North America. 



103 (22) Pseudopodia delicate, filiform, usually branched, and pointed. 



Family EUGLYPHIDAE . . 104 



104 (107) Shell flexible, transparent Pamphagus Bailey . . 105 



105 (106) Shell spherical Pamphagus hyalinus Ehrenberg 1838. 



The aperture of the shell is very large and capable of great 

 dilation. Protoplasm is clear, colorless. Nucleus spherical; 

 contractile vacuole single. Pseudopodia numerous, straight, and 

 pointed. Found in clear water. Diameter of shell 30 to 48 M. 



FIG. 324. Pamphagus 



hyalinus. cv, contractile vacuole. 

 (After Leidy.) 



X 260. 



106 (105) Shell ovoid or elongate. 



Pamphagus mutabilis Bailey 1853. 



Body very changeable in form. Protoplasm enclosing brilliant 

 granules. Nucleus large, spherical. Contractile vacuoles, one or 

 two. Found in clear water. Length of shell 50 to 70 M. 



FIG. 325. Pamphagus mutabilis. X 165. (After Penard.) 



107 (104) Shell rigid . . 108 



108 (113) Shell retort-shaped 109 



