114 BRITISH FBESHWATEK EHIZOPODA. 



P. compressa the tests have a considerable range of 

 form and the aperture is certainly flexible; the former 

 has a peculiar and characteristic test and is also 

 remarkable as containing, according to Penard, 

 numbers of a parasitic bacillus in the plasma. Further 

 investigations are desirable to ascertain if these are 

 invariably present. 



P. fnlt'ci and P. fascicularis are stable forms usually 

 easily identified; the test of P. gracilis, however, is 

 found in a wide range of forms to which at present 

 exact limits can hardly be ascribed, but they cannot 

 well include the form described by Schulze as P. 

 lageniformis.* 



SYNOPSIS OF THE BRITISH SPECIES. 



Test of medium size, sub-spherical or ovoid, not compressed ; 

 covered with fine quartz grains. (1) P. gracilis. 



Test small, pyrif orm, not compressed ; usually having a few 

 large adherent quartz grains. (2) P.fulva. 



Test of medium size, dark in colour, slightly compressed ; 

 usually covered thickly with diatom valves. (3) P. horrida. 



Test variable in size, pyriform, not compressed ; aperture 

 bordered by a collar. (4) P. fascicularis. 



Test moderately large, smooth, not compressed, covered by 

 a thick layer of small silicious particles. (5) P. orcheri. 



Te^t ovoid, of medium size, compressed; aperture flexible, 

 oval or linear. (6) P. compressa. 



1. Pseudodifflugia gracilis Schlumberger. 

 (Plate L, figs. 6-9, and PI. LI, figs. 10 and 11.) 



Pseudodifflugia gracilis 



SCHLUMBERGER in Ann. Sci. nat. (3) III (1845), p. 254. 



LEIDY (pars) Freslrw. Rhiz. N. Amer. (1879), pp. 198-201, pi. xxxiii, 



ff. 18-20 (? 21-24, 26, 27) ; in Proc. Acad. Philad. 1879, p. 163. 

 HITCHCOCK Synops. Freshw. Rhiz. (1881), p. 33. 

 TARANEK in Sitzb. bohm. Ges. Wiss. 1881, pp. 224, 233. 

 TARR in Rep. N. York State Mus. XXXV (1884), p. 167. 

 BLOCHMANN (pars) Mikr. Thierw. Siisswass. (1886), p. 14, pi. i, f. 32 ; 



ed. 2 (1895), p. 18, pi. i, f. 25. 



* ' Archiv f. mikros. Anat.' XI, p. 125, pi. vii, ff. 6-8. 



