26 AKCELLA. 



panded and circular base, which is inferior, convex at 

 the border, and concavely inverted infundibuliform cen- 

 trally to the mouth. Dome evenly convex or angularly 

 faceted or concavely pitted at the summit and sides ; the 

 facets or pits variable in number, bounded by prominent 

 folds and ranged in two or three circles. Mouth circular, 

 mostly entire, border rarely slightly crenulated. Sarcode 

 mass oblately spheroidal, colorless, except from food. 

 Pseudopods digitate, color of test, from colorless to 

 brown and deep blue. The shell sometimes appears like a 

 truncated pyramid, with angular outline, such forms may 

 be regarded as a variety angulosa. Size : breadth, 48// 

 to 152/x ; height, 36/* to I2p ; mouth, 12/* to 48/. Yery 

 common. 



Hob. Ooze of stagnant water and on submerged 

 aquatic plants. 



discoides. SYN. : A. discoides, peris tic ta, Ehr. ; A. 

 Homoiochlamis discoides, Ehr. ; A . Heterocosmia peristicta, Ehr. 



Shell circular, shield-shaped, usually with the length 

 from one-fourth to one-third of the breadth ; dome low, 

 evenly convex to the rounded, or slightly expanded and 

 rounded, basal-border ; base, mouth, and color of shell as 

 in A. vulgaris. Breadth, Y2// to 264^ ; height, 20/* to 

 80// ; width, 20// to 80//. 



Hob. Everywhere in association with A. vulgaris. 



Arcella, mitrata. 



Shell mitriform or balloon-shaped, obpyriform or poly- 

 hedral, higher than the breadth of the base, widest at or 

 near the middle, more or less contracted or sloping in- 

 wardly toward the base ; dome mostly inflated ; summit 

 and sides evenly rounded or depressed into broad, angu- 



