42 BRUITSH FRESHWATER RHIZOPODA. 
ovoid form of the test and the polygonal (usually 
hexagonal) aperture; the surface of the test may or 
may not be mamillated; the aperture may be plain 
or lipped; the test varies in length from 108 pw to 
160 » and is about one-tenth less in diameter than 
in length. 
In var. ininor (the “petite varieté” of Penard) the 
test is not mamillated and the aperture is invariably 
lipped; the length of the test is from one-tenth to 
one-third greater than the diameter; the aperture, 
usually more or less hexagonal, may be four- or five- 
sided or even somewhat lobed, this appearance being 
caused by the occasional convexity of its sides. 
If it were not for the fact that Penard has found 
intermediate forms this variety might be taken for an 
autonomous species. 
The elongated form of test with a diameter about 
three-quarters of the length is that usually met with. 
It also occurs on the Continent of Europe, in the 
Kastern United States (often plentifully), and in India. 
8. Difflugia constricta var. spinifera Playfair. 
(Fig. 172.) 
Echinopyxis aruleata (Ehrenb. sp.) 
CaRTER in Ann. Nat. Hist. (1) XIII (1864), p. 29, pl. i, £. 8. 
Difflugia mursupiformis 
Watuicn in Ann. Nat. Hist. XTII (1864), p. 241, pl. xvi, f. 5. 
Diffingia evnstricta 
Leripy (pars) Freshw. Rhiz. N. Amer. (1879), pl. xviii, figs. 45-57. 
CasH (pars) Brit. Freshw. Rhiz. II (1909), pl. xix, f. 17, and f. 69 
in text. 
Diffingin constricta var. spinifera 
PiayrarR in Proc. Linn, Soc. N.S. Wales. XLII, 4 (1918), p. 647, 
pl. xxxvi, f. 6. 
The variety thus named is the spined form of 
D. constricta as illustrated by Cash in Vol. II, fig. 69, 
p. 58, and Pl. XIX, fig. 17. Many spined forms occur 
which (as stated, loc. cit. p. 57) are indistinguishable 
from Ceutropyeis uculeata (Ehrenb.) Stein; on the 
other hand spineless forms of this species, C. aculeata 
