12 BRITISH FEESH WATER RH1ZOPODA. 



Var. lacustris (Penard). (Plate XIX, figs. 1 and 2 ; 

 and fig. 40 in text.) 



Difflugia pyrif en-mis var. lacustris PENARD in Eev. Suisse 



Zool. VII, 1 (1899), p. 24, t. ii, f. 11; Faune Rhiz. 



Leman (1902), p. 222, f. 8 (p. 218) ; Sarc. grands Lacs 



(1905), p. 21, f. (p. 22) ; and in Pr. R. Soc. Ediub. XXV 



(1905), pp. 594, 597; AVERINTZEV in Trudui S.-Peterb. 



Obshch. XXXVI (1906), 2, p. 198; and in Zool. Anzeig. 



XXXI (1907), p. 244; SCHOUTEDEN in Ann. Biol. 



Lacustre, I, 3 (1906), p. 346 ; THIEBAUD & FAVRE in Ann. 



Biol. Lacustre, I, 1 (1906), pp. 76, 82 ; ZSCHOKKE in Arch. 



Hydrobiol. II (1906), p. 3; SCHNEIDER in Arch. Biontol. 



II, 1 (1908), p. 57. 

 Difflugia piriformis var. lacustris PENARD in Rev. Suisse 



Zool. XVI, 3 (1908), pp. 466, 468. 



Test elongated, pyriform, or sub-cylindrical, slightly 

 wider above than below, variable in length ; composed 

 of chitinous material with some incrustation of sand- 

 grains (which are smallest about the mouth) in addition 

 to angular siliceous scales, more or less transparent; 

 the neck fortified by a ring of quartz-like particles, 

 or a few of these only, irregularly disposed, and com- 

 paratively large, projecting outwards beyond the mar- 

 ginal line. The nucleus situated, as in other Difflugise, 

 in the upper part of the body ; the pseudopodia digi- 

 tate, simple, not numerous. 



Dimensions : Length 120-1 60 /A, or more. 



In Cheshire ponds, frequent, along with the variety 

 venusta and others. Probably very widely distributed. 

 Pond at Chipperfield, Herts (A. Earland). Loch Ness, 

 Scotland, in deep water (G. 8. Went). 



This variety differs from others which have a semi- 

 transparent chitinoid test in its elongated cylindrical 

 or sub-cylindrical outline and uniformly arched crown, 

 whilst its possession of large and prominent sand- 

 grains, disposed in a ring about the neck, is a specially 

 distinguishing feature. Penard ('Faune Rhiz. Leman,' 

 p. 221) describes the var. bryophila, which is found 

 amongst mosses in woods. It closely resembles var. 



