GENUS PSEUDODIFFLUGIA— PSEUDODIFFLUGIA GRACILIS. 199 



Arncebas. They further remark that the animal is covered with a shell 

 composed of foreign substances cemented together, and having a single 

 aperture. The species indicated by them under the name of Pleuroplmjs 

 spliccrica* is described as possessing a spherical shell composed of silicious 

 particles, and measuring 0.02 mm. The figure accompanying their descrip- 

 tion represents a nearly globular shell of coarse sand, with granular fila- 

 mentous pseudopods extending like the rays of an Actinophrys. 



I have many times met with inconspicuous rhizopods with a shell 

 approximating in character that of the Difflugias, but with delicate filament- 

 ous pseudopods. I have suspected them to belong to the genus Pseudo- 

 difflugia of Schlumberger or of Pleurophrys of Claparede and Lachmann. 

 They occur in the ooze of ponds, and are of such obscure character, that 

 unless attention is directed to them, they are liable to be overlooked or mis- 

 taken for the excrement of worms or other masses of dirt They present 

 considerable variety in form, size, color, and exact composition of the shell, 

 and such intermediate gradations that 1 have been disposed to view most 

 of them as pertaining to the same species. 



Pseudodifflugia gracilis, as I have supposed it to be, is of quite 

 variable form, proportions, and size. Commonly it is ovoid, with the mouth 

 at the narrower pole, but sometimes is ovate, oval, oblong, or sub-pyriform. 

 See figs. 18-21, pi. XXXIII. The mouth is circular, and appears to be 

 contractile or dilatable, so that it varies in size according to its condition. 

 Sometimes it is oblique or sub-terminal, as seen in fig. 22, and occasionally 

 I have found individuals with the shell somewhat curved and the mouth 

 oblique, as represented in fig. 24. Usually the shell is of uniform trans- 

 verse diameters, but sometimes is more or less compressed, as represented 

 in the specimen of figs. 26, 27. The fundus of the shell is broad and 

 mostly evenly convex, but sometimes rather flattened. 



The color of the shell is variable, usually some shade of brown, but 

 often colorless. In composition it often appears membranous, and incorpo- 

 rated with variable proportions of fine dirt and sand. Sometimes the dis- 

 tinctly visible sand grains are minute and scattered, and sometimes they are 

 larger and closely cemented together, as is ordinarily the case in most 

 species of Difflugia, and as seen in the figures last referred to. 



* fitudes Infusoires, 455, pi. xxii, fig. 3. 



