130 MR. G. H. WAILES ON FRESHWATER RHIZOPODA 



The processes are usually nine in number, occasionally twelve ; the various 

 forms depicted by Leidy were found, except those with a flattened crown. 



Diameter 120-135 [i ; aperture 35-40 ya. 



DistrUmtion. Long Island, N.Y.; New Jersey (30); Pennsylvania (30); 

 Michigan (41) ; Ohio (28). 



Arcella discoides, Elirenlerg. 

 Leidy, pi. ^8. figs. 14-21, 2-3-29 (30). 



Grenerally distributed but not very numerous. 



Size variable, but usually 130-160 fx in diameter ; aperture 60-80 fx ; 

 height about one-third of the diameter. 



An individual from Lakehurst was similar to Leidy's fig. 21 : diameter 

 52 fi ; height 11 jjl. 



A. hemisph^rica, Perty (36). 

 A. vulgaris, Ehrenb. pars, Cash (10). 

 Not coDjmon ; diameter 42-50 yu. 



A. MITRATA, Leidy. 



Leidy, pi. 29. figs. 1-21 (30). 



Abundant in sphagnum, especially at Lakehurst. The structure of the test 

 is similar to that of A. vulgaris^ but the alveoli (0"8 /^ diam.) are surrounded by 

 six small pores (?) making a pattern similar to that on one form of Cyplio- 

 deria [vide 45. pi. ii. fig. 10 h) ; Cushman & Henderson (18) give micro- 

 photographs of it. 



Diameter 70-176 /i ; aperture 22-50 yit; base 50-120 ya ; height 55-150 ytt. 



The test may be circular or polygonal ; the aperture may be with or 

 without a secondary invagination and it may be circular or crenulate ; there . 

 appears to be no interdependence among these variations. 



A. POLYPORA, Penard (36). 



Leidy, pi. 28. fig. 22 (30). 

 Not uncommon in Split Rock Lake and Van Cortlandt Park ; the largest 

 individuals probably belong to a distinct species. 

 Diameter 230-340 fi ; aperture 126-190 yu,. 



A. VULGARIS, Ehrenberg. 



Leidy, pi. 27. figs. 1-3, .5-14, 17, 20-22 (30). 



This species is not very plentiful ; the test consists of a chitinous envelope 

 stiffened externally by bars 0"8 yu, apart, disposed in three parallel rows 

 inclined at 60° from eacb other. This structure is described by Penard (36); 

 Cushman & Henderson (18) give microphotographs of it. As in the case of 



