226 FRESH-WATEE RHIZOPODS OF NORTH AMERICA. 



The size of the shell ordinarily ranges from 0.05 mm. to 0.083 mm. 

 long, 0.04 mm. to 0.071 mm. broad, and 0.0161 mm. to 0.033 mm. thick. 



Assulina seminulum is common in sphagnum, and is often one of the 

 most abundant forms. It is remarkable that among the specimens com- 

 monly observed comparatively few are living. The same observation has 

 been made by Mr. Archer, who recently, as I, described the species as a 

 new one of Euglypha. 



TRINEMA. 



Greek, trl, three; noma, thread.* 



Animal provided with a hyaline, pouch-like shell, with its long axis 

 inclined or oblique, and with the mouth subterminal. Dome obtusely 

 rounded; mouth inverted, circular, minutely beaded at the border. Struc- 

 ture of the shell in the smallest forms mostly appearing homogeneous, but 

 in the larger composed of circular plates arranged in alternating series, and 

 often appearing with a beaded margin. Sarcode and pseudopods as in 

 Euglypha. 



Animal when in movement with the body inclined, the mouth being 

 anterior and downward; the fundus directed upward and backward. 



TRINEMA ENCHELYS. 



Plate XXXIX. 



Trineme. Dujardin: An. Se. Nat. 1836, v, 198, 205, pi. ix, fig. Aa-Ad. 



Difflugia Enchelys. Ehrenberg: Infusiousthierchen, 1838, 132, Taf. ix, Fig. iv. — Pritchard: Hist. Infusoria, 



1861, 553, pi. xxi, fig. 19. 

 Trinema. Dujardin: An. Sc. Nat. 1838, x, 261, note to 263.i 

 Arcella hyalina. Ehrenberg : Abh. Ak. Wis. 1841, Taf. i, ii, Fig. 31, Taf. iii, vi, Kg. 6, Taf. iv, i, Fig. 34, 



a, b, v, Fig. 3; 1856, Tafel (p. 377), Fig. 2, 3. Monatsbericbte, 1848, 215; 1849, 98. 

 Trinema acinus. Dujardin: Infusoires, 1841, 249, pi. iv, fig. 1. — Perty: Kenut. kleinst. Lcbeusformen, 



1852, 187.— Fresemus: Abh. Senck. Naturf. Gesell. 1856-8,223, Taf. xii, Fig. 25-27.— Clapa- 



rede and Lackmann: Infus. et FJiizopodes, 1858-9, 455.— Leidy: Pr. Ac. Nat. Sc. 1874, 227; 



1877, 321.— Schulze : Arch. inik. Anat. 1875. 104, Taf. v, Fig. 9-11. 

 Arcella constricta. Elrrenberg: Abh. Ak. Wis. 1841, 410, Taf. iv, i, Fig. 35. Mikrogeologie, 1854, Taf. 



xxxix, iii, Fig. 3. 

 Arcella Nidus Pendulus. Ehrenberg: Abh. Ak. AVis. 1841, 410, Taf. iii, i, Fig. 48. 

 Arcella Disphoera. Ehrenberg: Abh. Ak. Wis. 1841, 410, Taf. iv, ii, Fig. 12. 

 Anrlla caudicieola Ehrenberg: Monatsb. 1848, 215, 218. Abh. Ak. Wis. 1871, Taf. ii, Fig. 31. 

 Arcella Enchelys. Ehrenberg : Mikrogeologie, 1854, Taf. xxxviii, Fig. 5, Taf. xxxix, iii, Fig. 4. Monatsb. 



1845, 319; 1848, 215; 1849, 299; 1851, 228; 1853, 182, 266, 332; 1854, 710; 1856, 337, (Tafelj 



Fig. 2. 



* Named from the circumstance that commouly three pseudopodal threads are observed projected 

 from the mouth of the shell. 



tin 183S, Dujardin employed only the gallicized name of Trineme for the little rhizopod; and 

 not until 1838, after the publication of Ehrenberg's 'Infusionsthiereheu,' did he use the name Trinema. 

 In I In- note indicated he speaks of Ehrenberg's DiJJluyia Enchelys as clearly being the same as his Trinema. 

 Not until 1811, in his ' Histoire des Infusoires,' does he give to it the specific name of T. acinus. 



