136 BRITISH FRESHWATER RHIZOPODA. 



circular oral aperture being situated at the extremity 

 of a short and singularly unsymmetrical neck. 



Genus 27. HELEOPERA Leidy, 1879. 



Difflugia (NeMa) LEIDY in Pr. Acad. Philad. 1874, p. 157. 

 Nebela LEIDY in Pr. Acad. Philad. 1876, p. 119. 

 Heliopera LEIDY Freshw. Rhiz. N. Amer. (1879), p. 16. 



Test chitinous, varying in colour from greyish-rose 

 or deep purple, more or less convex at the mouth in 

 broad view, or truncated, with rounded corners ; the 

 crown hemispherical and nearly always rough with 

 adhering sand-grains, which in some individuals are 

 piled up conically. The surface covered with trans- 

 parent amorphous scales, the edges of which often 

 overlap, and present a meshwork of fine but usually 

 indistinct, dotted or interrupted lines. The mouth 

 narrow, elliptic, notched in narrow lateral view. The 

 plasma as in Nebela and Hyalosphenia ; the nucleus 

 single, situated posteriorly as in those genera; the 

 pseudopodia variable in number, thin, digitate or 

 branching. 



1. Heleopera sylvatica Pehard. 

 (Plate XXIX, figs. 10-12.) 



Heleopera petricola LEIDY (pars) Freshw. Rhiz. N. Amer. 

 (1879), p. 165, t. xxvi, if. 16-19. 



Heleopera sylvatica PENARD in Jahrb. nassau. Yer. Naturk. 

 XLIII (1890), p. 71 ?; in Mem. Soc, Geneve, XXXI 

 (1890), 2, p. 168, t. vii, ff. 79-94 ; in Arch. Sci. nat. (4) 

 VII (1899), p. 253; and Faune Rhiz. Leman (1902), 

 p. 389, ff. 1-4 (p. 390) ; AVEEINTZEV in Trudui S.-Peterb. 

 Obshch. XXXVI (1906), 2, p. 255 ; SCHOUTEDEN in. Ann. 

 Biol. Lacustre, I, 3 (1906), p. 357. 



Test transparent, oval in broad view, compressed, 

 narrower in proportion to its length than in the pre- 

 ceding species, and regular in contour, the sides curving 

 evenly downwards to the distinctly convex mouth ; its 

 substance chitinous, covered externally with minute 



