42 BRITISH FRESHWATER RHJZOPODA. 



IRELAND. Mayo. 



Owing to the small size and transparency of the 

 test the details of its construction are not easily seen; 

 in its often un symmetrical outline and irregular aper- 

 ture it closely resembles Assnlina muscorum when the 

 coloured membrane which lines the test and forms the 

 irregular margin of the aperture in that species is 

 wanting or is dissolved away; the often irregular 

 arrangement of the scales near the fundus and aper- 

 ture of the test is another point of resemblance 

 between the two species ; the similarity of the nuclei 

 is also very evident. Taking all these points into 

 consideration it might perhaps be considered a variety 

 of AssuHna muscorum rather than a true Euglypha. 



It is very widely distributed and in our experience 

 always associated with A. muscorum. 



It occurs on the continent of Europe, in N. and S. 

 America, and in Java. 



Genus 33. PLACOCISTA* Leidy, 1879. 



Euglypha CARTER (pars) in Ann. Nat. Hist. (3) XV (1865), 



p. 290. 



Placocista LEIDY Freshw. Rhiz. N. Ainer. (1879), p. 221.' 

 Placocysta BLOCHMANN Micr. Thierw. Siisswass., ed. 1 



(1886), p. 14. 



Test ovoid, hyaline, compressed ; lenticular in trans- 

 verse section ; composed of oval or subcircular sili- 

 cious scales regularly imbricated; aperture wide, 

 linear, with flexible undulate borders ; nucleus large, 

 placed posteriorly ; contractile vesicles two or more ; 

 plasma grey or colourless, partially filling the test, the 

 central zone loaded with granules, and may contain 

 Zoocklorellse living symbiotically ; pseudopodia filose, 

 branching and numerous, generally arising from a 

 protruded portion of plasma. 



The members of this genus are distinguished from 

 the Evglyphx by the linear orifice and the absence of 



* " Greek, plax, a plate ; Tcista, a box " (Leidy). 



