264 FEESH-WATEE EHIZOPODS OF NOETH AMEEICA. 



at times shows slight changes in the outline, while its contractile vesicles 

 pursue their usual rhythmical movements, at each moment as one collapses 

 giving the whole body a gentle quiver. 



ACANTHOCYSTIS. 



Greek, akantha, a thorn; knslis, a cyst. 

 Trichoda: Schrank, 1803. Aotinophrys : Ehrenberg, 1833. Acanthocijslis : Carter, 1864. 



Animal Actinophrys-like in general appearance. Body spherical, soft, 

 composed of finely granular protoplasm mingled with variable proportions 

 of bright-green and colorless corpuscles, the former at times absent, also 

 containing diffused oil molecules, a central nucleus, together with vacuoles, 

 and a variety of food materials commonly in the form of balls. Exterior 

 of the body invested with numerous delicate, silicious rays, implanted by 

 minute basal disks, and. ending in a simple, pointed or furcate extremity; 

 also giving off numerous delicate, soft rays like those of Actinophrys; fur- 

 ther enveloped by a layer of protoplasm, rising in pointed processes on the 

 rays, and pervaded by a multitude of exceedingly minute, linear particles; 

 the enveloping layer sometimes absent. 



ACANTHOCYSTIS CH^TOPHORA. 



Plate XEIII, tigs. 1-6. 



Trichoda chwtophora. Schrank : Fauna Boica, iii, 2, 1803, 93. 



Actinophrys viridis. Ehrenberg: Abh. Ak. Wis. Berlin, 1833, 228; Infusionsthierchen, 1838, 304, Taf. 



xxxi, Fig. vii. — Dujardin: Infusoires, 1841, 267. — Perty : Kennt. kleinst. Lebensformen, 



1852, 159.— Pritchard : Hist. Infus. 1861, 560.— Micrographic Dictionary, pi. 23, fig. 6. 

 Acanthocystis turfacea. Carter: An. Mag. Nat. Hist. 1864, xiii, 36, pi. ii, fig. 25. — Archer: Quart. Jour. 



Mic. Sc. s, 1870, 27; xvi, 1876,361. — Hertwig and Lessor: Arch. mik. Anat. x, 1874, Suppl. 



204.— Greeff : Arch. mik. Anat. xi, 1875, 30, Taf. i, Fig. 1-4. 

 Acanthocijslis viridis. Greeff: Arch. mik. Anat. v, 1869, 481, Taf. xxvi, Fig. 8-17. — Greenacher : Zeits. 



wis. Zool. xix, 1869, 289, Taf. xxiv, Fig. 1-3.— Schneider : Ibidem, xxi, 1871, 505.— Leidy : 



Proc. Ac. Nat. Sc. 1874, 166. 

 Acanthocystis pallida. Greeff: Arch. mile. Anat. v, 1869, 489, Taf. xxvii, Fig. 19. 

 Acanthocystis (viridis) turfacea. Greeff: Arch. mik. Anat. xi, 1875, 3, Taf. i, Fig. 1-4. 



Body spherical, usually bright green from the presence of chlorophyl 

 corpuscles, mingled in variable proportion together w r ith colorless ones ; 

 sometimes colorless from the absence of the former. Nucleus central, com- 

 monly obscured from view by the surrounding constituents. Silicious or 

 spinous rays of two kinds : the one long, comparatively strong and acutely 

 furcate at the free end ; the other short, very delicate, and widely furcate at 

 the free end, and sometimes altogether absent. Soft rays simple, granular, 



