50 BRITISH FRESHWATER RUIZOPODA. 



The form of the internal diaphragm, which is 

 situated centrally, leaving an opening on either side, 

 distinguishes this species from P. com/>revsa (Carter) 

 Cash which has the diaphragm stretching across the 

 whole width of the neck of the test, with an orifice 

 on one side only ; instances occur in which the tests 

 of the latter have no obvious external- features to 

 mark the neck and indicate the form of the dia- 

 phragm; in these cases it may be necessary to 

 immerse the tests in oil-ot-cloves or Canada balsam 

 to enable the structure of the diaphragm to be clearly 

 seen and their identity established. To this occasional 

 external similarity of the two species the paucity of 

 records of P. rhnmbleri, in the British Isles may be 

 due. 



The form of the test distinguishes it from P. elisa 

 which has a similar type of diaphragm. 



Rhumbler's name of P. compressa is preoccupied 

 by the species so named by Carter in 1864, described 

 on p. 62 of Vol. II, and the present name is suggested 

 on p. 162 of the same volume. 



Genus 23. CRYPTODIFFLUGIA Penard, 1890. 



Cryptodifflugia PENAIJD in Mem. Soc. .Geneve, XXXI, i, n 

 (1890), p. 168. 



In Vol. Jl one species belonging to this genus, 

 C. oviformis Penard, is described by Cash ; since then 

 three other species have been recorded from the 

 British Isles. 



All the members of the genus are remarkably shy 

 and seldom display their pseudopodia whilst under 

 observation. 



The following description of the life-cycle in this 

 genus from the observations by Prandtl * is given 

 by Minchinf : 



* Prandtl, EL, "Der Entwicklungskreis von Allogromia sp .,'' ' Archiv fur 

 Protistenkunde,' IX, p. 1 (1907). 



t Minchin, E. A., 'Introd. to the Study of the Protozoa.' London, 1912. 



