112 W. ARCHER. 



Quadrula symmetrica, Eilh. Schulze,^ = Difflugia sym- 

 metrica (Wallich), (PI. VIII, fig. 6) 



is a Difflugian form which, in my opinion. Prof. Schulze was 

 amply justified in taking as the type of a distinct genus, 

 the differential characters of course residing in the test, as the 

 animal portion or sarcode body offers no very tangible distinc- 

 tion from an ordinary Difflugia ; there are occult differences, 

 no doubt, else how the wide distinction when "fully formed ?" 

 The first to recognise this species seems to have been Dr. 

 WalHch ;" I have myself met with the same form, though 

 by no means frequently, in various collections, and would 

 have proposed its being considered the type of a distinct 

 genus, especially on my recently finding a further species of 

 the same structure as regards the test. For I would quite 

 agree with the view now expressed by Schulze that only 

 Lobosa, whose habit is to build up or affix foreign particles, 

 should be retained in the genus Difflugia proper. At the same 

 time it is an open question whether all these which do so should 

 be relegated thereto ; as for instance the peculiar and remark- 

 able seemingly uniqu.e structure of the test of the common 

 form Difflugia spiralis, although it often appends externally 

 arenaceous particles, would, 1 fancy, justify its separation. 



In Quadrula the test is formed of hyaline angular plates, 

 apposed laterally and in mutual contact. They are ordi- 

 narily square or slightly oblong, but occasionally in some 

 parts of the test they may be triangular, trapezoid, or even 

 more or less irregularly figured, this variation in shape from 

 the square being in order to adapt themselves to the charac- 

 teristic total figure of the test and so as to leave no mutual 

 intervals or lacunae. In Quadrula symmetrica the test is of 

 a compressed pyriform figure,with straight longitudinal axis, 

 and with a broad elongate neck abruptly but roundly trun- 

 cated ; the transverse view oval ; the broad " mouth" offers two 

 "lips" (on aline Avith the broader sides), each with a convex 

 margin, between which on each side (on a line with the nar- 

 rower sides of the test) is an intervening hollow. At the 

 broader inflated portion of the test the hyaline component 

 plates are larger and more regularly square in figure ; on 

 forming the neck or approaching thereto it is that they 

 diminish in size or alter in figure according to the exigencies 

 of the contour so as still to remain in mutual apposition and 

 at same time build up the characteristic figure of the species. 



1 Sihultze's ' Arcbiv f. Mikr. Anat.,' Bd. xi, p. 329, t. xviii, f. 1—6. 



2 'Ann. Nat. Hist.,' vol. viii (1864), p. 815. 



