GENUS AECELLA— AECELLA MITEATA. 175 



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

 of Claparede and Laehmann,* and I have suspected that they may be the 

 same. 



ARCELLA M1TRATA. 



Plate XXIX. 

 Arcella milrata. Leidy : Proc. Ac. Nat. Sci. 1876, 56. 



Shell mitriform or baloon-shaped, obpyriform or polyhedral, higher 

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

 contracted or sloping inwardly toward the base ; 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 infundibuliform ; 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 ectosarc 

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



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

 to 0.168 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 mitrala, 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, Nuphar 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 s. 1. Iiifus. et Rhizopodes, 1858, 9, 443, pi. xxii, fig. 5. Hertwig and Lesser: Archiv 

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



