98 FRESH- WATER RHIZOPODS OP NORTH AMERICA. 



membrane incorporated with Variable proportions of sand grains, as 

 seen in figs 13-17, pi. XVI. Specimens, found in sphagnous swamps, 

 sometimes consist of chitinoid membrane incorporated with variable .pro- 

 portions of diatoms, or fragments of the same, with sand grains and other 

 particles of a less determinate character, as represented in 'figs. 9, 10, 18, 

 19, pi. XVI. Specimens are also fomid, in the same situations, composed 

 almost entirely of diatoms, as represented in figs. 2 1 , 22. The larger shells 

 of Difflugia gldbulosa, composed of quartz-sand, are commonly colorless, 

 but may be more or less yellowish or brownish, apparently due to ferrugi- 

 nous staining. Occasionally specimens are seen, like those of figs. 23, 24, 

 in which the cementing material of the sand particles exhibits a deeper 

 stain of the same kind. The smallest shells are more commonly of a 

 yellowish hue. 



In my experience it has occurred to meet with dead shells of D. 

 gldbulosa more frequently than with living specimens. 



The sarcode of D. gldbulosa, independent of food contents, is colorless. 



Difflugia gldbulosa through intermediate forms merges into D. pyriformis, 

 and I suspect also into 2). Idbostoma. The small oblate-spheroidal forms, 

 with inflected base, especially when mainly composed of chitinoid mem- 

 brane, are scarcely distinguishable from Arcellas. I have also seen speci- 

 mens in which the mouth was more or less eccentric, and I was uncertain 

 whether to refer them to the species under consideration, or whether to 

 regard them as pertaining to Difflugia constricta, or the spineless form of 

 Centropyxis aculeata. 



The range of size is considerable. The smallest specimens, found 

 among moist earth, measured about 0.036 mm. long by 0.03 mm. broad, 

 with the mouth 0.015 mm. The largest specimens, from the ooze of a pond, 

 measured 0.3 mm. in diameter, with the mouth 0.16 mm. 



DIFFLUGIA PYRIFORMIS. 



Plates X; XI; XII, figs. 1-18; XV, figs. 32,33; XVI, fig. 38; XIX, figs. 24-26. 



Difflugia. Leolero : Mdm. Mus. Hist. Nat. 1815, ii, 474, pi. 17, fig. 



Diffl/iigia pyriformis. Perty : Mittheil. Natnrf. Gesells. Bern, 1848, 168 ; Kennt. Tdeinst. Lebensformen, 



1852, 187, Tab. ix. Fig. 9.— Pritohard : Hist. Infusoria, 1861, pi. xxi, fig. 17.— Carter : An. 



Mag. Nat. Hist, xii, 1863, 249; xiii, 1864, 21, pi. i, fig. 1.— Wallich: An. Mag. Nat. Hist. 



xiii, 1864, 240, pi. xvi, figs. 9, 10, 39, 40.— Ehrenberg : Ab. Ak. Wis. Berlin, 1871, 264.— 



Leidy : Pr. Ac. Nat. Sc. 1874, 14, 79 ; 1877, 307. 

 Difflugia proteiformis. In part of Lamarck and Ehrenberg = Loclerc's figs. 2, 3, pi. 17, M6m. dii Mus. 



d'Hist. Nat. ii, 1815. 



