QUADRULA. SYMMETBICA. 131 



Test in broad view pyriform, the crown semi-circular; 

 much narrower at the mouth, which has a slightly 

 convex outline; the sides tapering convexly down- 

 wards to the base ; the structure compressed laterally. 

 The transparent chitinous plates arranged in oblique 

 series across the surface; usually smaller about the 

 mouth than above, and not infrequently out of position. 

 Plasma very clear, containing chlorophyl-corpuscles 

 with other elements; the pseudopodia (usually 3-5) 

 digitate; the single nucleus prominently situated in 

 the upper region of the body. 



Dimensions : Variable ; average length about 96 ft ; 

 breadth 60-70 ft ; in dorsal (transverse) view about 

 40 ft. 



FIG. 102. Test of Quadrula symmetrical, x 375. 



In marshy ground amongst Sphagnum, etc. ; some- 

 times in moss growing on moist r.ocks ; abundant and 

 widely distributed. 



This beautifully -transparent species is usually abun- 

 dant in boggy ground, where Sphagnum abounds. The 

 disposition of the plates is not always symmetrical; 

 they are sometimes seen pressed out of position, with, 

 as a consequence, overlapping edges ; frequently also 

 the edges project beyond the margin of the test. 



Two forms are found sometimes in the same gather- 

 ing one considerably broader in proportion than the 

 other, but not otherwise essentially differing. 



Penard, in a paper communicated to the Royal 

 Society of Edinburgh (March, 1905), " Sur les Sarco- 



