42 BRITISH 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 /a to 

 160 JJL and is about one-tenth less in diameter than 

 in length. 



In var. minor (the " petite variete " 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 

 Eastern United States (often plentifully), and in India. 



8. Difflugia constricta var. spinifera Playfair. 



(Fig. 172.) 



Echinopyxis aculeata (Ehrenb. sp.) 



GARTER in Ann. Nat, Hist. (1) XIII (1864), p. 29, pi. i, f. 8. 

 Difflugia mnrsupiformis 



WALLICH in Ann. Nat. Hist. XIII (1864), p. 241, pi. xvi, f. 5. 

 Diffliiyia constricta 



LEIBY (pars) Freshw. Rhiz. N. Amer. (1879), pi. xviii, figs. 45-57. 



CASH (pars) Brit. Freshw. Rbiz. II (1909), pi. xix, f. 17, and f. 69 



in text. 

 Difflngi'i. constricta var. spmifi'm 



PLAYFAIR in Proc. Linn/Soc. N.S. Wales. XLII, 4 (1918), p. 647, 

 pi. xxxvi, f. 6. 



The variety thus named is the spined form of 

 I), 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 Cenfropi/xis aculeata (Ehrenb.) Stein ; on the 

 other hand spineless forms of this species, C. aculeata 



