Geographical Distribution.—This species was originally described from North America (in which it is apparently common) and occurs also in Europe. I have seen Indian specimens from the following localities:—Bengal, Calcutta and neighbourhood; Rajshahi (Rampur Bhulia): E. Himalayas, Gangtok, Native Sikhim (alt. 6,150 feet) (Kirkpatrick, Stewart): Punjab, Lahore (Stephenson).
Biology.—P. diffusa in Lower Bengal is a cold-weather species. It is remarkable for the enormous number of gemmules it produces and is usually found either on floating objects such as the stems of certain water-plants, or on stones or bricks at the edge of ponds.
33. Plumatella allmani, Hancock. ([Plate IV], figs. 3, 3 a.)
Plumatella allmani, Hancock, Ann. Nat. Hist. (2) v, p. 200, pl. v, fig. 3-4, pl. iii, fig. 2-3 (1850). Plumatella allmani, Allman, Mon. Fresh-Water Polyzoa, p. 106, fig. 16 (1857). Plumatella elegans, id., ibid. p. 107, pl. viii, figs. 6-10. Plumatella lucifuga ("forme rampante") Jullien, Bull. Soc. zool. France, x, p. 114 (1885).
This species is closely allied to P. diffusa, from which it differs in the following characters:—
(1) The zoarium never covers a large area and as a rule grows sparingly and mainly in two directions.
(2) The zoœcia are more irregular in shape, not so distinctly elbowed, smaller; they have a much more prominently keeled ridge. The great majority of them are constricted at the base and taper towards the orifice. In young zoaria they are almost colourless but in older ones there is a band of not very dense pigment round the base of the vertical limb.
(3) The free statoblasts are comparatively large and usually show a tendency to taper at the extremities, often being almost rhomboidal in form. The swim-ring does not extend so far over the dorsal surface as it does in those of P. diffusa; the "cells" of which it is composed are small.
Type not in existence.
I have seen every gradation between this form and Allman's P. elegans.