GENUS CTPHODERIA— CYPHODERIA AMPULLA. 203 



XXXIV. The long axis of the shell forms a line curving' upwardly and 

 backward from the mouth. In the ordinary position of movement of the 

 animal, the mouth is directed downward on a horizontal plane, while the 

 body of the shell is directed backward, with but slight inclination from the 

 same plane. 



The sides of the shell are commonly evenly convex, but occasionally 

 somewhat flattened or slightly tapering toward both poles. The fundus is 

 usually evenly convex, but sometimes flattened, and frequently more or less 

 prolonged and narrowed at the summit into a nipple-shaped process, as seen 

 in figs. 4—8. 



The mouth of the shell is circular, and exhibits a beaded margin more 

 or less distinct. Schulze describes it as possessing a delicate and structure- 

 less membranous expansion or zone;* but this, if it exists, escaped my 

 attention, or was taken for an expansion of sarcode at the root of the 

 pseudopods. 



The shell is straw-colored or pale yellowish, and often entirely color- 

 less. It is transparent, and apparently composed of chitinoid membrane, 

 as in Arcella. It exhibits a structure of variable distinctness, consisting 

 of exceedingly minute hexagonal elements, alternating with one another, 

 and arranged in spiral rows. Ordinarily the shell has a more or less 

 uniform punctate appearance; but when the structure is more than usually 

 distinct, the arrangement of hexagons is very obvious. The outlines of 

 the hexagons will appear single and dark, or double and clear, as seen in 

 fig. 16, according to the focus in which they are viewed. In several 

 instances it has seemed to me as if the hexagons were externally faceted 

 in inclined triangular planes from common centres. 



The soft contents of the shell of Cyphoderia occupies its capacity in 

 varying extent, as in the case of Euglypha. Sometimes it entirely fills the 

 shell, sometimes it is more or less contracted in an intermediate position 

 from the sides, and it is not unfrequently more or less contracted from the 

 fundus. In the last condition, the mass is usually attached to the dome of 

 the shell by a pair Or more of fine thread-like extensions of the sarcode, as 

 is so conspicuously observed in Hyalosphenia, and as represented in figs. 

 13, 14. 



A large clear nucleus occupies the fundus of the body, and generally 



* Archiv f. luik. Anatomic, 1675, 111, Taf. v, 20. 



