126 BRITISH FEBSHWATEE EHIZOPODA. 



1. Clypeolina marginata Penard. 

 (Plate LIU, figs. 5 and 6.) 



Clypeolina marginata 

 Penabd in Rev. Suisse Zool. IX (1901), p. 237 ; Faune Rhiz. Leman 



(1902), pp. 459-461, 4 figs. ; Savcodines grands Lacs (1905), pp. 



69-61, 109, 7 figs.; Sarcodines in Cat. Invert. Suisse (1906), p. 93; 



in Arch. Protist. VIII (1906), pp. 66-85, 10 figs.; in Rev. Suisse 



Zool. XVI (1908), p. 466. 

 AvBEiNTZBFF in Trudui S.-Peterb. Obshch. XXX 71, ii (1906), 



p. 273. 

 ScHOUTBDEN in Ann. Biol, lacustre, I (1906), p. 363, f. 33. 



Test ovoid, compressed, consisting of outer and 

 inner envelopes ; the outer envelope formed of two 

 equal valves of a chitinous material with an admixture 

 of small scales and silicious grains, yellow or brown in 

 colour and becoming darker with age ; the transverse 

 section lenticular ; the inner envelope consisting of a 

 thin, flexible, colourless membrane closely investing 

 the plasma; the aperture terminal, wide, linear; the 

 plasma with clear, limpid ectoplasm and pale blue endo- 

 plasm containing numerous small globules; nucleus 

 large, ovoid or spherical, placed nearly centrally 

 and containing an irregularly-shaped nucleole; a single 

 large contractile vesicle and numerous vacuoles usually 

 present ; pseudopodia numerous, long, filose, straight, 

 often alternately branched. 



Length 80-150 /x, but usually 120-135 /x,; breadth 

 rather more than half the length. 



Habitat. — -Aquatic vegetation in lakes and marshes. 



England. — Norfolk (Gash). 



For a detailed study of this species, Penard (' Archiv 

 fiir Protist.,' 1906) should be consulted; these later 

 researches modify to some extent his description of 

 the genus and species written in 1902. This is the 

 only known Ehizopod provided with a bivalve test, 

 the two valves fitting together like those of a mussel, 

 but without any hinge ; multiplication takes place by 

 the division of the internal membrane in a longitudinal 

 direction, and each of the individuals thus formed 



