GENUS AECELLA— ARCELLA ARTOCREA. 179 



Size. — Breadth at lateral border 0.144 mm. to 0.176 mm.; breadth at 

 base 0.1 12 mm. to 0.136 mm.; height 0.04 mm. to 0.06 mm.; width of mouth 

 0.02 mm. to 0.028 mm.; elevation of the same 0.012 mm. to 0.024 mm. 



Locality. — Absecom pond, New Jersey. 



Arcella artoerea (pi. XXX, figs. 1-9) is most nearly related to 

 A. discoides, but the sarcode mass is of a bright-green color from the 

 presence of an abundance of chlorophyl corpuscles entering into the com- 

 position of the endosarc. It is rare, as I have found it only in Absecom 

 pond, and in the wet sphagnum skirting the same, and here seldom. 



The shell is comparable in shape to an ordinary pie, a turban, or to a 

 low and round-crowned hat, and is of a bright raw sienna-brown color of 

 varied shades. 



The shell is commonly between a fourth and a third of the height 

 of the breadth, but also occurs of greater or less proportionate height. 

 Viewed from above or below (figs 1, 3, 5, 7), the outline is mostly cir- 

 cular, but is sometimes oval, quadrately oval, or more or less constricted, 

 so as to be biscuit-shaped. The lateral, prominent, more or less angular 

 border is elevated from a fourth to neai'ly half the height of the shell. 

 The dome is evenly convex, or it is mammillated or conversely pitted. 

 The base is centrally inverted in a concave funnel-like manner. The 

 mouth is circular, or sometimes oval, and is entire. It is elevated from a 

 fourth to nearly half the height of the shell, and sometimes appears slightly 

 everted into the funnel formed by the base of the shell. Around the 

 mouth there is a circular row of bright points which appear to be minute 

 tubercles. 



The sarcode forms a lenticular mass of variable proportionate size, 

 occupying the central portion of the shell (fig. 1). It is attached in 

 the usual manner by threads of ectosarc, and the pseudopods are like 

 those of other forms of Arcella. The endosarc is bright green, from the 

 presence of chlorophyl corpuscles measuring about g^th of an inch in 

 diameter. 



Arcella artoerea is a comparatively large form, in this respect also 

 related to A. discoides. It ranges in breadth from ^- th to —th of an inch, 

 and in height from ^th to — th of an inch. 



