54 BRITISH FBESHWATEE EHIZOFODA. 



Ges. Wiss. 1881 (1882), p. 227; GREEFP in Sitzber. Ges. 

 Nat. Marburg, 1888, p. 107 ; HARYEY in Amer. Natur. 

 XXII (1888), p. 72 (as ascula) ; CEKTES in Mission scient. 

 Cap. Horn, VI (1889), 3, Prot., p. 13; PENARD (pars) in 

 Mem. Soc. Geneve, XXXI (1890), 2, p. 148, t. iv, ff. 92, 

 94-96, 98, 99; in Amer. Natur. XXV (1893), p. 1071 ? ; 

 in Arch. Sci. nat. (4) VII (1899), p. 268; Faune Rhiz. 

 Leman (1902), p. 296, ff. 1-4 (p. 297) ; and in Jrn. R. 

 Micr. Soc. 1907, p. 277; CASH in Tr. Mauch. Micr. Soc. 

 1891 (1892), p. 48 ; LEVANDER in Acta Soc. Fauna Fenn. 

 XII (1894), 2, p. 18 ; and op. cit. XX (1901), 8, pp. 8, 10 ; 

 DADAY in Termesz. Fiizetek, XXI (1898), Suppl. pp. 6, 9 ; 

 EYFERTH Naturgesch. mikr. Siisswass. ed. 3 (1900), p. 

 263; LAGERHEIM inForh. Geol. Foren. Stockholm, XXIII, 

 6 (1901), p. 472; AVERINTZEV iiiTrudui S.-Peterb. Obshch. 

 XXXVI (1906), 2, p. 181; SCHOUTEDEN in Ann. Biol. 

 Lacustre, I, 3 (1906), pp. 341, 344; MURRAY in Ann. 

 Scott. Nat. Hist. 1907, p. 94. 



Test hemispherical, with a slightly concave base, the 

 crown regularly arched, incrusted with fine sandy or 

 muddy particles, opaque; the mouth (inferiorly situ- 

 ated) triangular or irregularly trilobed, or roughly 

 quadrangular, and never invaginated as in Arcdla. 

 Nucleus single ; pseudopodia normal [?]. 



Dimensions : Diameter of base about 90 /x ; elevation 

 of crown 40-45 //,. 



In marshy places ; also in tufts of moss and liver- 

 wort growing on moist rocks ; and in shady woods ; 

 frequent. 



The form with triangular mouth is probably the one 

 most frequent with us. Occasionally in Sphagnum the 

 mouth is irregularly quadrate. In no case is the rim 

 inverted as in some examples figured by Leidy, which 

 belong to Centropyxis. 



23. Difflugia constricta (Ehrenb.) Leidy. 



(Plate XIX, figs. 14-20; PI. XXII, figs. 12-14; 



and figs. 66-69 in text.) 



Arcella constricta EHRENBERG in Abh. Akad. Wiss. Berlin, 

 1841, p. 410, t. iv, f. 35, and t. v, f. 1 ; op. cit. 1871 



