44, BRITISH FRESHWATER RHIZOPODA. 
Wallich in 1864 gave the name Difflugia marsupi- 
formis to the spined forms of this species and the 
name D. cassis to the small and usually spineless 
forms; since then, however, both forms have usually 
been grouped together under the name D. constricta 
(Ehrenb.) Leidy. : 
In the Clare Island Survey report Penard* has the 
following note:—‘‘In reality these two Rhizopoda 
(Difflugin constricta add Centropyxis aculeata) are 
practically inseparable; and in my opinion it would 
be better to transfer Difflugia constricta at once to the 
genus Centropyxis, which, by its peculiar shape and 
the special disposition of the peristome, etc., is removed 
from all the Difflugiz.” 
Genus 18a. BULLINULA Penard, 1911. 
Bulinella Penarp in Jrn. R. Micr. Soc. 1907, pp. 274, 278. 
(pre-occupied in Mollusca, 1891.) 
Bullinula Pewarp in Brit. Antarct. Exped. I, Biol., 6 (1911), 
p. 226. 
Test smooth, ellipsoidal, flattened on one face, 
formed of silicious plates cemented upon a thin 
pellicle; the flattened face pierced by an elongated 
narrow slit constituting a peristome with a smooth 
inferior lip and an overhanging superior lip; nucleus 
single; pseudopodia digitate or spatulate, simple or 
branched. 
The genus contains only one species, B. indica 
Penard, which is widely distributed throughout the 
world but does not usually occur very numerously. 
As in the genus Plagiopyzxis, the aperture ig often diffi- 
cult to detect and the opacity of the test prevents 
observation of the plasma. The name Bulinella, being 
occupied in another Phylum, was altered to Bullinula. 
* Wailes & Penard in ‘Proc. Roy. Irish Acad.’ Clare Isl. Survey, Pt. 65 
(1911), p. 22, note. 
