GENUS AECELLA— ARCELLA MITEATA. 175 



the kind just described appear to me to resemble the PseudocMamys patella 

 of Claparfede and Lachmann,* and I have suspected that they may be the 

 same. 



ARCELLA MITEATA. 



Plate XXIX. 

 Arcella mitrata. Leidy : Proc. Ac. Nat. Soi. 1876, 56. 



Shell mitriform or baloon-shaped, pbpyriform or polyhedi-al, higher 

 than the breadth of the base, widest at or near the middle, more or less 

 contracted or sloping inwardly toward the ba,se ; dome mostly inflated ; 

 summit and sides evenly rounded or depressed into broad angular facets, 

 bounded by prominent folds ; base rounded at the border, inverted con- 

 cavely infundibuhform ; mouth circular, crenulated, mostly everted into 

 the inverted funnel. Sarcode mass spheroidal, usually connected with 

 the mouth by a cylindrical neck, and attached by threads of ectoparc 

 to the interior of the shell. Pseudopods up to half a dozen or more. 



Size. — Height from 0.08 mm. to 0.18 mm. ; breadth at base 0.072 mm. 

 to 0.1 68 mm. ; breadth at dome 0.084 mm. to 0.2 mm. ; width of mouth 0.02 

 mm. to 0.08 mm. ; elevation of mouth from base 0.02 mm. to 0.024 mm. 



Locality. — Abundant in Absecom pond ; also found in ponds at Atco, 

 Malaga, and other places. New Jersey; Tobyhanna, Pocono Mountain, 

 Pennsylvania; and ponds in the Uinta Mountains, Wyoming Territory. 



Arcella mitrata, though by no means so common as the forms 

 which have been viewed as characteristic of A. vulgaris and A. discoides, 

 is rather frequent in the ponds of sphagnous and cedar swamps of New 

 Jersey. I have found it especially abundant in Absecom pond, so rich in 

 other rhizopods. I found it also in a pond in which grew a profusion of 

 the Yellow Pond-lily, NupJiar advena, at an altitude of about 10,000 feet, 

 in the Uinta Mountains, Wyoming. 



Arcella mitrata, as represented in the figures of pi. XXIX, departs 

 from the form of A. vulgaris in a direction opposite to that of A. discoides. 

 Viewed from above or below (figs. 1, 3, 5, 7, 10), it is commonly circular, 

 though often more or less modified by angular projections of the base or 



* Etudes 8. 1. Infus. et Ehizopodes, 1858, 9, 443, pi. xxii, fig. 5. Hertwig and Lesser: Archiv 

 f. mlkr. Anat. 1874, 100, Taf. iii. Fig. 1. 



