200 FRESH-WATER RHIZOPODS OF NORTH AMERICA. 



In several instances I found individuals which I viewed as pertaining 

 to the same animal, in which the shell was mainly granular and translucent, 

 but had large sand grains accumulated at the extremities, as seen in fig. 25. 



In those specimens in which the shell is not too thoroughly incorporated 

 with dirt or sand, the interior sarcode becomes more or less visible, and is 

 seen to be of variable extent in relation to the capacity of the shell. A 

 large clear spot in the fundus of the sarcode indicates the presence of a 

 nucleus, and a darker intermediate zone the accumulation there of fine oil 

 molecules. The lower region is likewise observed to contain vacuoles and 

 portions of food. 



The pseudopods of Pseudodifflugia gracilis are numerous, finely fila- 

 mentous and branching. They are sometimes observed diverging from the 

 mouth in profuse bunches ; at other times in a few filaments. See figs. 18— 

 28. On one occasion I observed a number of pseudopods run together into 

 a broad patch of protoplasm, which involved, within a vacuole, two green 

 algous cells, as seen in fig. 22. 



The movements of the animal are exceedingly slow, and it often 

 requires long watching to observe it project the pseudopods. 



Pseudodifflugia is more closely related with Pamphagus and Cypho- 

 deria than with the Heliozoa. Subsequently to Claparede and Lachmann, 

 other investigators have described Rhizopods which they refer to species 

 of Pleurophrys, but which I suppose to pertain to Pseudodifflugia, and 

 most of them to P. gracilis. 



Mr. Archer* described a form which he refers to Pleurophrys sphcerica, 

 though of larger size and otherwise different from that of the former 

 authors. Schulze considers the determination incorrectf The shell is 

 represented as spheroidal, brown, and composed of granular matter, with 

 a size of ^th of an inch. 



150 



Fig. 19 represents an individual of nearly the size and constitution 

 of that just indicated, as described and figured by Mi*. Archer. It is, 

 however, of ovoid shape, and measures 0.16 mm. long by 0.1 mm. broad. 

 Both forms I view as pertaining to Pseudodifflugia gracilis. 



In the same memoir, Mr. Archer indicated two other forms as pertain- 

 ing to Pleurophrys, with the names of P. amphitremoides and P. fulva.% 



* Quart. Jour. Micr. Sc. 1869, fig. 1, pi. xx ; 1870, 121. 

 t Arcliiv f. mikr. Anatomie, 1875, xi, 122. 

 } Quart. Jour. Micr. Sc. 1870, 121, 122. 



