DIPLOPHRYS AEOHEEI. 147 



The phenomena of multiplication by tetrad division 

 are entirely exceptional among the Kliizopoda. 



The colonies of embryos are very similar to those 

 reputed to belong to the Heliozoon Elseorhanis cincta 

 G-reefE, which however measure about 7 yu, in diameter 

 and contain yellow oil-like globules. Archer's Gijsto- 

 phrys ocalea (' Qrt. Jrn. Micr. Sci.,' vol. ix (1869), 

 PI. XX, fig. 3) may possibly represent this organism. 



Genus 50. AMPHITREMA Archer, 1869. 



Amphitrema Aechbe in Qrt. Jrn. Mior. Sci. (n. S.) IX (1869), 



p. 397. 

 Ditrema Archer in Qrt. Jrn. Micr. Sci. (n. s.) XVIII (1877), 



p. 103. 



Test ovoid, symmetrical, compressed, composed of 

 a transparent membrane with or without adherent 

 extraneous particles ; provided with a small aperture 

 at each extremity ; plasma colourless, granular, usually 

 containing living Zoochlorella-cellB ; nucleus single, 

 placed centrally ; one or two contractile vesicles iisually 

 present; pseudopodiafilose, straight, sparsely branched, 

 radiating. 



Archer created the genus Ditrema to include D. 

 flavum, a species which is similar to those of the genus 

 Amphitrema except that the test is devoid of extraneous 

 adherent particles ; this seems an insufficient reason 

 for not including in a single genus species which are 

 so closely related. 



A. rhenianum Lauterborn does not properly belong 

 to this genus.* 



Synopsis of the British Species. 



Test brown, devoid of adherent particles. (1) A. flavum. 

 Test colourless, covered with foreign particles ; apertures 



furnished with external collars. (2) A. wrightianum. 



Test colourless, covered with foreign particles; apertures 



without collars. (3) A. stenostomd'. 



'■ *Peiiardj ' Eevue Suisse ZdoI.^,' vol. xix, 191] . 



