ASSULINA. 49 



Genus 34. ASSULINA Ehrenberg, 1872. 



Difflugia (pars) Ehrenberg Ber. Akad. Berlin, 1848, p. 379. 

 Euglypha (pars) Lbidy Proo. Acad. Philad. 1874 (1875), 



p. 226. 

 Assidina (pars) Bhrenberu Abh. Akad. Berlin, 1871 (1872), 



p. 246. 

 Assulina Leidy Freshw. Etiiz. N". Amer. (1879), p. 224. 



Test brown or colourless, ovoid, glabrous, com- 

 pressed, formed of elliptical, imbricated, silicious 

 scales, disposed more or less regularly in diagonal 

 rows ; aperture oval, terminal, truncate or with a 

 short neck, bordered by a thin chitinous dentate 

 membrane ; plasma grey or colourless, granular ; 

 nucleus large, placed posteriorly ; contractile vesicles 

 one or more ; pseudopodia filose, more or less nume- 

 rous, divergent, sometimes branched. 



Compared with the members of genus Eughjpha the 

 Assulina, have less numerous and less branched pseudo- 

 podia, the plasma is less clear and contains more fine 

 granules often of a sandy colour. The dentate or 

 jagged, transparent and nearly colourless membrane 

 bordering the aperture together with the highly com- 

 pressed test and narrow aperture are distinctive of 

 this genus. The brown colour of the tests, when 

 present as it usually is, sufl&ces to distinguish the 

 genus easily ; this colour is due to a brown chitinous 

 membrane which lines the tests, and also partly 

 perhaps in many cases to the cementing material 

 joining the scales together. The deposits of this 

 cement are abnormally thick and usually hide the 

 true shape of the oval scales, giving them the false 

 appearance of a tile-like arrangement similar to that 

 of a house-roof, the scales appearing to overlap from 

 the fundus downwards, whilst in reality they are 

 arranged the reverse way. The test of A. seminulum 

 .var. scandinavica is, however, an exception, as it is 

 often colourless, and the outlines of its broadly-oval 

 or sub-circular scales are plainly seen. The form of 



VOL. III. 4 



