34 BRITISH FRKSH WATER RHIZOPODA. 



Test spheroidal in form, flattened on the ventral 

 side, of a dark-grey colour with black markings ; the 

 outer envelope formed of small globular masses of 

 organic matter mixed with silicious particles ; the inner 

 membrane extremely fine ; aperture normally circular 

 but capable of assuming various forms or becoming 

 linear ; plasma clear, colourless, granular, containing 

 food-particles, starch -grains, granules of excretion, 

 and occasionally a few rectangular crystals ; nuclei 

 small, about 100 in number, each containing a single 

 nucleole ; several contractile vesicles usually present ; 

 pseudopodia conical, wide at the base with pointed 

 extremities, one or two in number, 'rarely displayed. 



Diameter 75-130 JJL, usually about 100 /A. Nuclei 

 3-5 p, in diameter. 



Habitat. Mosses, dry and submerged. 

 IRELAND. Achill Island, Mayo (Penard}. 



In submerged mosses a large form is found about 

 190-200 p, in diameter, occasionally attaining to 400 /x. 



1. Centropyxis aculeata var. discoides Penard. 

 (Plate LXI, figs. 1 and 2.) 



Centropyxis aculeata var. discoides 

 PENARD Faune Rliiz. Leman (1902), pp. 305-306, 7 figs. ; Sarcodines 



in Cat. Invert. Suisse 0^05), p. 59. 



DADAY in Zool. Jabrb., Syst. XXV (1907), 2, p. 249. 

 WAILES in Jrn. Linn. Soc.. Zool. XXXII (1912), pp. 123,128; (1913), 



p. 212. 



Test circular, discoid, larger and more compressed 

 than in the type, either brown and chitinous or grey 

 and covered with silicious grains and plates, with or 

 without spines, which if present are few in number; 

 aperture less eccentric than in the type ; nucleus 

 single, large, granular ; plasma and pseudopodia as in 

 the type. 



Diameter 150-300 /M; thickness about one-quarter 

 the diameter ; aperture about one-third the diameter. 



Habitat. Aquatic vegetation. 



