1 20 FRESH- WATER EHIZOPODS OF NORTH AMERICA. 



are sometimes extended upward even to the ends of the spines projecting 

 from the fundus. Mostly perfectly clear, under high powers of the micro- 

 scope they appear uniformly and exceedingly finely granular. When 

 much extended, they often exhibit the entrance, along their axis, of coarser 

 granules from the endosarc. 



Dr. Wallich, who first described D. corona, views it as a variety of what 

 he calls the subspecies Difflugia globularis. 



In the original notice of the latter,* as D. globulosa, Dujardin describes 

 the shell as corneous and nearly globular, and accompanies the account 

 with figures, one of which, representing a side view, is ovoid, with an oval 

 mouth without crenulation. In the 'Histoire Naturelle des Infusoires,' he 

 describes the shell as brown, globular or ovoid, and smooth. 



In the 'Proceedings of the Dublin Microscopical Club,' 1866, p. 53, it 

 is stated that Mr. Archer, among other Rhizopods exhibited one that he 

 "would refer somewhat doubtfully to Difflugia corona." He remarks, "If 

 this be D. corona, Dr. Wallich's figure is too regular and symmetrical, too 

 diagrammatic, the adherent foreign particles too accurately adapted, and too 

 much of one size, and the horns too short." According to my experience, 

 Dr. Wallich's figure is a fair representation of the species, and Mr. Archer's 

 criticism leads me to suppose that he had under comparison an irregular 

 specimen, and not one of the usual character. 



Difflugia corona ranges from the 1 5 th to the -Uh of an inch. It is one 

 of the most characteristic and beautiful forms, and is also common in 

 many localities. It is found living in the surface mud at the bottom of 

 ponds and ditches, or among the dirt adherent to submerged aquatic plants. 

 It feeds on algse and apparently also on decaying vegetal matter. 



DIFFLUGIA CONSTFJCTA. 



Plate XVIII. 



Areclla constricta, Ehrenberg: Abk. Akad. Wis. Berlin, 1841, 410, Taf. iv, i, Fig. 35, Taf. v, Fig. 1. 

 Arcella limata. Ehrenberg: Ibidem, 1841, 410; 1671, 259, Taf. iii, ii, Fig. 3, 4. 



Arcclla Arctiscon. Ehrenberg : Microgeologie, 1854, 108, 171 ; Abh. Ak. Wis. 1871, 258, Taf. iii, ii, Fig. 17. 

 Arcella gualimalcnsis. Ehrenberg : Microgeologie, 1854, 364 ; Ab. Ak. Wis. 1871, 259, Taf. iii, ii, Fig. 1G ; 



Nordpolarfahrt, 1874, Taf. iii, Fig. 35. 

 Difflugia marsitpiformis. Wallich : An. Mag. Nat. Hist, xiii, 1864, 241, 244, pi. xvi, figs. 3-5.— Leidy : Pr. 



Ac. Nat. Sc. 1877, 307. 

 Difflugia prolciformis, subspecies D. marsupifonm is. Wallich: Ibidem. 



Difflugia marsupiformis, variety D. cassis. Wallich : Ibidem, fig. 6. — Leidy : Pr. Ac. Nat. Sc. 1877, 321. 

 A. Homaocltlamys constricta. Ehrenberg: Ab. Ak. Wis. 1871, 244. 



♦An. Sc. Nat. viii, 1837, 311, pi. 9, fig. 1. 



