ARCELLA VULGARIS. 121 
not frequently extended beyond the outer margin of 
the test. Contractile vesicles, numbering four or more, 
situated near the outer margin of the endoplasm. 
Dimensions: Diameter of test variable, averaging 
70 or more; the mouth 12-20 pn. 
_ Common and universally distributed, most frequent 
in the ooze and amongst surface vegetation in ponds. 
The colour of the test varies from a clear hyaline or 
pale yellowish tint (in the young state) to a deep brown. 
The membrane is thin and phable, becoming brittle 
with age. Conjugation has been observed to take 
place, accompanied by fusion of the protoplasm, but 
this is not of frequent occurrence. “ Budding” is 
more common. 
Var. angulosa (Perty) Leidy. (Plate XV, figs. 12 
and 16.) 
Arcella angulosa Prrry Kenntn. kleinst. Lebensf. (1852), 
p- 186; Maca in Atti Soc. Ital. XXI (1878), pp. 314, 315. 
Arcella vulgaris var. angulosa Luipy Freshw. Rhiz. N. Amer. 
(1879), t. xviii, ff. 8-18. 
Arcella costata (Ehrenb.) Prnarp in Rev. Suisse Zool. IX 
(1901), p. 237, and Faune Rhiz. Léman (1902), p. 401, ff. 
Test smaller than in the type, faceted, forming a five- 
to eight-sided figure, with obtuse angles; the angles 
rising obliquely from the broad base to the narrower 
depressed summit. Mouth central; protoplasm, nucleus, 
and contractile vesicles as in the type. 
Dimensions - Diameter of test averaging 30-40 u. 
Occurring occasionally in marshy places, amongst 
Sphagnum, and in ponds. 
Var. gibbosa (Penard) G. 8. West. (Plate XV, figs. 11 
and 17; and fig. 19 in text.) 
Arcella gibbosa Panarp in Mém Soc. Phys. Genéve, XXX], 
no. 2 (1890), p. 155, t. v, ff. 96-99; t. vi, £..1. 
Arcella vulgaris var. gibbosa G. 8. Wzst in Journ. Linn. 
Soc., Zool. XXVIII (1901), p. 314, and op. cit. XXIX 
(1903), p. 109. 
