ARCELLA DEXTATA. 



127 



Dimensions : Diameter 95 /a ; length of spines 

 15-17 /x ; mouth 30 /*, diam. 



Ponds in Cheshire, rare. 



FIG. 21. Arcella dentata (face view), a Swiss form, after Penard. x 250. 

 22 23 



FIGS. 22 AND 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 LEIDY in Proc. Acad. Nat. Sci. Phil. 1876, 

 p. 57; Freshw. Rhiz. N. Atner. (1879), p. 178, t. xxx, 

 ff. 1-9; CORRADO in Boll. Scient, I, an. 2 (1880), p. 47; 

 ROLLESTON Forms Artim. Life, od. 2 (1888), p. 901 ; 

 SCOURFIELD in Proc. Zool. Soc. 1897, p. 788 ; G-. S. WEST 

 in Journ. Linn. Soc., Zool. XXVIII (1901), p. 315, 

 t. xxviii, f . 2 ; ? PENARD Faune Rhiz. Lenian (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 



