208 FRESH-WATER RHIZOPODS OF NORTH AMERICA. 



Assvlina alvcolata, A. amphora, A. areolata, A. Florida; A. moluccensis, A. rcctangularis, A. Soberti MiiUcr, 



and A. tubcrculata. Ehrenberg : Abh. Ak. Wis. 1871, 246. 

 Set igwclla acantophora and S. setigcra. Ehrenberg: Ibidem, 247. 



Difflugia Shannoniana. Ehrenfcerg : Zweite dcutsche Nordpolarfahrt, 1874, Taf. iii, Fig. 18. 

 Difflngia subacuta. Ehrenberg : Ibidem, fig. 19. 



Shell transparent, colorless, mostly regularly ovoid, often oblong ovoid, 

 sometimes flask-shaped ; in transverse section circular, and rarely slightly 

 compressed ; fundus broad, obtusely rounded, rarely subacute ; oral 

 extremity narrowest, often more or less tapering. Mouth truncating the 

 oral pole, circular, surrounded with from four to twelve 1 angular, den- 

 ticulate points formed by the lowest circular series of the plates of the 

 shell.* Plates of the shell generally oval or ovate or cordate?, arranged 

 in longitudinal rows in alternating series, and overlapping at the contiguous 

 borders, so as to produce hexagonal areas included in zones of minute 

 elliptical areola?. Fundus of the shell in the best developed forms mostly 

 provided with from four to six spines, as appendages of certain of the 

 plates, usually nearly equidistant and straight, of variable length and 

 robustness, sometimes divergent, occasionally convergent, not unfrequently 

 irregular ; in the smaller and less well developed forms altogether absent. 



Size. — Ranging from 03 mm. long by 0.018 mm. broad to 0.152 mm. 

 long by 0.088 mm. broad. 



Locality. — The largest and spinous forms in the ooze of ponds, ditches, 

 etc.; the smallest spineless forms among alga?, mosses, and other plants in 

 bogs, meadows, and other moist or damp situations. Pennsylvania, New 

 Jersey, Maine, Florida, Nova Scotia, Wyoming Territory. 



Euglj |»lia alveoSata, in what I have regarded to be its variations 

 of form under different conditions, is perhaps the most common species. It 

 varies considerably in size, proportions, exact shape, and other characters, 

 and indeed the extreme variations have probably as much claim to be 

 regarded as species as most of the forms of Euglypha I have viewed as 

 such. See figs. 1-18, pi. XXXV. 



Commonly the shell of Euglypha alveolata is regularly egg-shaped, 

 with the narrow pole truncated by the mouth, as seen in figs. 1, 2, 4; 

 frequently, however, the oral pole is more tapering and prolonged, and 

 it is rarely somewhat flask-shaped, as represented in fig. 3. The fun- 



* The number of points to the mouth of the shell of Euglypha is generally uncertain, from the 

 difficulty of fixing the individual in such a position as to see them all distinctly. As the shell is 

 usually viewed, the mouth can be seen only from one side, and it requires much time and patience to 

 ascertain the exact number of points which surround it. 



