12 ERITISH FRESHWATER EHiZOPODA. 



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

 and fig. 40 in text.) 



Difflugia pyriformis var. lacustris Penakd 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. Edinb. XXV 



(1905), pp. 594, 597 ; Avjsbintzev 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 & Favbe in Ann. 



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



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



II, 1 (1908), p. 57. 

 Difflugia piriformis var. lacustris Penaed 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 Difflugia.', 

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

 tate, simple, not numerous. 



Dimendons : Length 120-160^, or more. 



In Cheshire ponds, frequent, along with the variety 

 venusta and others. Probably very widely distributed. 

 Pond at Chipperfield, Herts {A. Earlaiid). Loch Ness, 

 Scotland, in deep water {G. S. Went). 



This variety differs from others M^hich 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. hryopliihi, Avhich is found 

 amongst mosses in woods. It closely resembles var. 



