RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 113 



Normally they may be said to run in longitudinal and trans- 

 verse series, but they may occasionally run obliquely, or even 

 an abrupt alteration of arrangement may occur, yet on the 

 whole all are nicely posed to produce the symmetrical charac- 

 teristic external aggregate contour of the test. A greater 

 disturbance of the symmetry of the plates may often take 

 place close to the edge of the "mouth/' where, whilst they 

 become smaller in size, they also suffer greater alterations of 

 individual figure so as to become adapted to the peculiar con- 

 tour, as described, of the frontal opening, the extreme edge 

 of which appears to form a thickened margin. These plates 

 are not very firmly combined, a moderate pressure sometimes 

 sufiices to dislocate them, and in abandoned tests one sees 

 often little accidental aggregations of these plates, lying often 

 superposed. 



The body-mass and its pseudopodia are like that of an 

 ordinary Difflugia. It does not quite fill the test ; often there 

 proceed a few slender sarcode processes therefrom to the test, 

 forming so many attachments ; in the posterior end occurs a 

 nucleus Avith nucleolus, and towards the anterior end may 

 sometimes be seen a few pulsating vacuoles. 



Quadrula irregularis, n.s.. Archer. 



Except in being smaller, corresponding to the smaller test, 

 there is not any distinction to be drawn from the sarcode 

 body, as just described, as regards the form I%ould here 

 record under the foregoing name, its diff"erences being in the 

 size and figure of the test ; still I would not be in the least 

 disposed to regard it as but a young form of Q. symmetrica, 

 I have taken this form from extremely remote localities, 

 both in Ireland and Scotland, and ever presenting the same 

 features, and I have likewise noticed a single example quite 

 identical with the British specimens on a slide of Nordstedt's, 

 the material having been collected in Italy, the Quadrula 

 accidentally present, indeed, as the slide Avas put up for a 

 Cosmarium. It is sometimes accompanied by Q. symmetrica, 

 but more frequently presents itself alone; it must, however, 

 be accounted rarer by a good deal than the typical species. 



This form is smaller than Q. symmetrica, quite without 

 any neck, the " mouth" being where a small chord seems, as 

 it were, cut off the globular, or perhaps somewhat compressed 

 test, nor are there any " lips'^ nor even any evident thickened 

 margin ; the mouth seems as it were but a cessation of the 

 component plates, but on the whole subcircular in outline. 

 As in the former, the typical form of the plates is square. 



