.174 FRESH-WATER RHIZOPODS OP NORTH AMERICA. 



inverted funnel of the mouth. As many as a dozen contractile vesicles may 

 sometimes be detected. Commonly I observed two nuclei, sometimes one, 

 and sometimes three. 



The size of the shell of Arcella discoides usually ranges from about 

 g^th to ^th of an inch in breadth, ^th to ^th of an inch in height, with 

 the mouth ^th to ith of an inch wide, and elevated above the base from 

 s^-th to .^.th of an inch. 



olJ5 1J00 



Among some Utricularia from Jacksonville, Florida, I found a num- 

 ber of specimens, viewed as pertaining to A. discoides, in which the base of 

 the shell was more widely and deeply concave than usual, as represented 

 in figs. 33, 36. In some of the individuals, the shell was circular; but, in 

 others, it was oval or quadrately oval. The mouth, also, was oval, but with 

 the long diameter crossing that of the shell, as seen in fig. 35. 



I have also occasionally met with Arcella discoides having an oval shell 

 in Absecom pond, New Jersey, as represented in fig. 34. From the same 

 locality I obtained several specimens, in which the shell had a somewhat 

 trilobate outline, as seen in fig. 38. 



In empty shells of Arcella discoides I have generally noticed a circle 

 of bright dots surrounding the mouth, as seen in figs. 34-38. Whether 

 these dots are pores or minute tubercles I have not ascertained. When 

 present in living specimens, they are entirely obscured from view by the 

 granular sarcode within the shell. Similar dots I have likewise noticed 

 in some of the specimens attributed to Arcella vulgaris, as represented in 

 figs. 4, 6. 



Occasionally I have observed small discoid Arcellas, measuring about 

 ji- th of an inch in diameter, such as ai*e represented in figs. 30, 31, which 

 I have supposed to be the young of Arcella discoides. The shell is trans- 

 parent, has a pale yellowish tinge, and is so delicate that traction of the 

 threads of attachment of the sarcode draws parts of the shell out of shape, 

 or at times bends the two sides toward each other. The mouth is indis- 

 tinctly seen ; a cancellated structure, if existing, is not evident ; and even 

 the shell itself, at times, requires attention to perceive it. 



The sarcode is colorless and granular, and usually exhibits two or 

 three contractile vesicles at a time. Mostly I detected no nucleus ; but 

 in several specimens I observed what I supposed to be one, measuring 

 3~th of an inch. The pseudopods are few and digitate. Specimens of 



