116 BRITISH FRESHWATER RHIZOPODA. 



Test a plain membranous structure encrusted in 

 most cases with a variable amount of extraneous 

 matter (sand-grains, diatom frustules, etc.) ; in others 

 semi-transparent, chitinoid, with few sand -grains; 

 multiform, mostly round in transverse or dorsal view ; 

 rarely compressed. 18. Difflugia. 



Test similar to the preceding, more frequently com- 

 pressed, with a constricted neck, and an internal 

 transverse loop, or bridge, dividing the neck at the 

 point of constriction. 19. Pontigulasia. 



Test membranous, transparent, smooth ; protoplasm 

 granular; pseudopodia one or more, central, digitate, 

 mobile, with a terminal apiculus ; and usually two 

 others (one on each side) issuing laterally, which are 

 thin, rigid, and tapering. 20. Difflugiella. 



Test unsymmetrical, usually forming a semi-spiral, 

 with vermiform or irregular surface-markings, semi- 

 transparent or opaque ; pseudopodia digitate. 



21. Lecquerensia. 



Test transparent, chitinoid .(rarely siliceous) sym- 

 metrical, compressed in transverse section, and con- 

 structed of minute circular, oval, or angular plates. 



22. Nebela. 



Test homogeneous, transparent, plain or pitted with 

 circular, polygonal, or irregular depressions, com- 

 pressed transversely. 23. Hyalosphenia. 



Test chitinous, transparent or semi-opaque, with a 

 faint irregularly - tesselated surfacing ; compressed 

 transversely ; 'the crown covered with a variable 

 number of angular sand-grains, or spined ; the mouth 

 convex. 24. Heleopera. 



Test hyaline, compressed or sub-orbicular, Composed 

 of rectangular plates disposed with more or less regu- 

 larity, transversely or in oblique series. 25. Qiiadrula. 



Test homogeneous, thin, 'transparent, flexible ; 

 pseudopodia lobate or digitate. 26. Cochliopodium. 



Test homogeneous, transparent, unsymmetrical ; 

 nucleus single ; pseudopodium single, broadly lobate or 

 cordate. 27. Leptochlamys. 



