46 BRITISH FRESHWATER RHIZOPODA. 
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. 7 
Genus 18b. PLAGIOPYXIS Penard. 
es Pewarp in Rev. Suisse Zool. XVIII, 4 (1910), 
p. 936. 
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 im 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 Triyonopyeis (Difflugia) areula. 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. /abinta, whose test is similar 
to that of P. callidu but with a wider aperture and 
no prolongation of the inner lip—some forms of it 
approach varieties of Difflugia constricta 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 
Punarp in Rev. Suisse Zool. XVIII, 4 (1910), pp. 936-940 iii 
ff. 8-10; in Brit. Antarct. Exped. I, Biol, 6 (bt) pp. ah S51 
Waites & Penarp in Proc. R. Ivish Acad. X 
18, 51, pl. vi, £. 304, b cad. XXXI, uxv (1911), pp. 9, 
