PYXIDICULA OPERCULATA. 19 
PritcHarD Hist. Infus. (ed. 2.] (1841), p. 198, pl. ii, f. 127; [ed. 3.] 
(1852), p. 433, pl. ii, f. 127. 
Battey in Amer. Jrn. Sci. Art, XLII (1842), p. 88, pl. ii, ff. 1, la. 
BRIGHTWELL Fauna Infus. H. Norfolk (1848), p. 36, pl. x, #. 10-12. 
Hextwie & Lesser in Arch. mikr. Anat. X (1874), Suppl. pp. 103-105. 
ARCHER in Qrt. Jrn. Micr. Sci. (2) XVII (1877), p. 110; in Proc. 
Dublin Mier. Club, ITI, 2 (1878), p. 228. 
BiocuMann Mikr. Thierw. Siisswass. (1886), p.11; ed. 2 (1895), p.15. 
PENARD in Rev. Suisse Zool. IX (1901), p. 288; Faune Rhiz. Léman 
(1902), pp. 413-414, 3 figs.; Sarcodinés in Cat. Invert. Suisse 
(1905), pp. 81-82. 
AVERINTZEFF in Trudui 8.-Peterb. Obshch. XX XI, 1 (1906), pp. 
144-145. 
ScHOUTEDEN in Ann. Biol. lacustre, I, 3 (1906), p. 333, f. 4. 
DoFLEIN in Sitzb. Ges. Morph. Minchen, XX XIII, 3 (1908), pp. 
116-117, f. 1 (7 figs.). 
Waites & Penarp in Proc. R. Irish Acad. XXXI, txv (1911), p. 19. 
Cyclotella operculata 
P BreBisson Consid. Diatom. (1838), p. 20. 
Kuetzine Bacill. oder Diatom. (1844), p. 50, pl. i, f. 1; ed. 2 (1865), 
p. 50, pl. i, f. 1. 
MENEGHINI in Atti Impl. Inst. Venuto, V (1846), pp. 88, 90; (transl. 
in) Bot. and Physiol. Memoirs (1846), pp. 385, 387. (Ray Soc.) 
8°. London. 
Perry Kenntn. kleinst. Lebensf. (1852), p. 200. 
Arcella patens 
CaRTER in Ann. Nat. Hist. (13), XIII (1864), pp. 61-62, pl. ii, f. 15. 
(Non Claparéde & Lachmann Etudes Inf. et Rhiz. (1859). 
Fia. 164.—Pyzidicula operculata: 1, wpper view; 2,sideview. x 1200. 
3, part of the test. x 4800. (After Penard.) 
Test discoid, circular, with narrow inverted margin 
forming a large circular orifice; formed of smooth, 
transparent, chitinous material finely punctate, be- 
coming darker or nearly brown with age; plasma clear, 
granular, nearly filling the test to which it is attached 
by numerous epipodes ; nucleus single, spherical, con- 
taining a large central nucleole; contractile vesicles 
usually numerous; pseudopodia short, lobose or digitate. 
} 9% 
