ARCELLA DENTATA. 127 
Dimensions : Diameter 95 w; length of spines 
15-17 w; mouth 30 » diam. 
Ponds in Cheshire, rare. 
Fie. 21—Arcella dentata (face view), a Swiss form, after Penard. x 250. 
22 23 
Fries. 22 anp 23.—Arcella dentata (side views): 22,a Swiss form, after 
Penard; 23, an American form, after Leidy. x 250. 
5. Arcella artocrea Leidy. 
(Figs. 24 and 25.) 
Arcella artocrea Lerpy in Proc. Acad. Nat. Sci. Phil. 1876, 
p. 57; Freshw. Rhiz. N. Amer. (1879), p. 178, t. xxx, 
ff. 1-9; Corrapo in Boll. Scient. J, an. Pe (1880), p . AT; 
Rouneston Forms Anim. Life, od. 2 (1888), a 901; 
ScourFigeLp in Proc. Zool. Soc. 1897, p. 788; G. S. Wzst 
in Journ. Linn. Soc., Zool. XXVIII (1901), p. 315, 
t. xxvii, f. 2; ? Penarp Faune Rhiz. Léman (1902), 
p. 404, ff., and p. 665. 
Test in height from one fourth to less than half the 
breadth ; the dome convex and even, or mamillated, 
or pitted ; basal border everted and rising from a 
quarter to nearly half the height of the test, obtusely 
