46 BRITISH FRESHWATER RH1ZOPODA. 



succeeded in doing so only after long-continued obser- 

 vation ('Revue Suisse Zool.' 1912). When mounted 

 in balsam the tests do not become any less opaque, 

 and only by carefully breaking them up can their 

 structure be ascertained. 



The aperture requires careful orientation of the test 

 to see it clearly ; the pores bordering its upper lip vary 

 in number and in their disposition, and occasionally 

 cannot be distinguished. 



Genus 18 b. PLAGIOPYXIS Penard. 



Plagiopyxis PENARD in Eev. Suisse Zool. XVIII, 4 (1910), 

 p. 986. 



Test of medium size, sub-circular in dorsal view, 

 ovoid in side view ; aperture linear, lunate, the inner 

 lip short or continued for a considerable distance 

 internally nearly parallel to the curvature of the test ; 

 plasma grey, granular; nucleus single; a single vacuole 

 usually present. 



Two species are included in this genus, P. callida 

 and P. labiata Penard ; the former is very similar in 

 form but smaller than Bullinula indica ; it also has 

 affinities with Trigonopy&i* (Difflugici) arcula. In none 

 of these species have the pseudopodia been observed, 

 except on one or two occasions by Penard. There is 

 no British record of P. lab'uifa, whose test is similar 

 to that of P. callida but with a wider aperture and 

 no prolongation of the inner lip some forms of it 

 approach varieties of Difflugia conxtricta so closely that 

 Penard has doubts as to whether it should not rather 

 be considered as a form or variety of that species. 



1. Plagiopyxis callida Penard. 

 (Plate LXI, fig. 7). 



Plagiopyxis callida 



PENARD in Rev. Suisse Zool. XVIII, 4 (1910), pp. 936-940, pi. viii, 



ff. 8-10; in Brit. Antarct. Exped. I, Biol., 6 (1911), pp. 250-251. 

 WAILES & PENARD in Proc. R. Irish Acad. XXXI, LXV (1911), pp. 9, 

 18, 51, pi. vi, f. 30 a, b. 



