170 FRESHWATER RHIZOPODS OF NORTH AMERICA. 



Biitschli,* after observing three individuals together, of Arcella vulgaris, 

 in conjugation, saw them separate without evident change, but later noticed 

 in one of them a number of cell-like bodies which occupied the space 

 between the sarcode mass and the shell The cell-like bodies afterward 

 assumed the appearance and movements of Amoebas, and escaped from the 

 mouth of the shell. He suspected them to be the young brood of the 

 Arcella, but their subsequent fate he did not determine. 



ARCELLA VULGARIS. 



Plates XXVII; XXVIII, figs. 1-7. 



Arcella vulgaris. Ehrenberg: Abh. Ak. Wis. Berlin. 1830, 40, 53, 61, 69, 70, 75, Taf. i, Fig. vi; 1831, 90; 

 1871, 234. Infusionsthierchen, 1838, 133, Taf. is, Fig. v.— Dujardin: Infusoires, 1841, 247, 

 pi. ii, figs. 3-5.— Perty : Kennt. kleinst. Lebensformen. 1852, 183, 186, Taf. ix, Fig. 1-3.— Carter: 

 An. Mag. Nat. Hist, xviii, 1856, 1*8, 221, pi. vii, fig. 79; xiii, 1864, 30, pi. ii, fig. 14.— Claparedo 

 and Lachmaim : Etudes Iiifus. Rbizop. 1858, 9, i, 444. — Pritcliard: Hist. Infusoria, 1861,555, 

 pi. xxi, figs. 7-9. — Wallick: An. Mag. Nat. Hist, xiii, 18j'4, pi. xvi, figs. 34-37. — Hertwig and 

 Lesser: Arch. mik. Anat. 1874,96.— Leidy: Pr. Ac. Nat. Sc. 1874, 14; 1876, 55.— Biitschli: Arch, 

 mik. Anat. 1875, 459, Taf. xxv. 



Arcella dentata. Ehrenberg: Ab. Ak. Wis. Berlin, 1830,40; 1831,90. Infusionsthierchen, 1838, 134, Taf. 

 ix, Fig. 7, except a. — Perty: Kennt. kleinst. Lebensformen, 1852, 186. 



Arcella hemispherica. Perty : Kennt. kleinst. Lebensformen, 1852, 186, pi. ix, fig. 5. 



Arctlla angulosa. Perty: Ibidem, 186. 



Arcella viridis. Perty?: Ibidem. 



Arcellina vulgaris. Carter : An. Mag. Nat. Hist, x viii, 1856, 247. 



A. Sticholepis vulgaris. Ehrenberg: Abh. Ak. Wis. Berlin, 1871,244. 



A. Somocochlamys angulosa. Ehrenberg: Ibidem. 



Shell hemispherical or campanulate; height about half the breadth 

 and more or less, widest across the usually slightly expanded and circular 

 base, which is inferior, convex at the border, and concavely inverted infun- 

 dibuliform centrally to the mouth. Dome evenly convex or angularly 

 faceted or concavely pitted at the summit and sides; the facets or pits 

 variable in number, bounded by prominent folds and ranged in two or 

 three circles. Mouth circular, mostly entire, rarely slightly crenulated at 

 the border. Sarcode mass oblately spheroid, colorless independently of 

 the color of the endosarc derived from the food, connected with the mouth 

 by a short cylindroid neck, and attached by divergent threads of ectosarc 

 to the inner surface of the dome. Pseudopods digitate. Color of the test 

 passing from completely colorless in the earliest condition, through various 

 shades of brown, to the deepest hue. 



Size.— Breadth 0.048 mm to 0.152 mm.; height 0.036 mm. to 0.072 

 mm.; breadth of mouth 0.O12 mm. to 0.048 mm.; elevation of mouth 0.006 

 mm. to 016 mm. 



*Archiv f. mik. Anat. xi, 1875, 459. 



