The transparent gla.s.sy ectocyst and strong furrowed keel of this species are very characteristic, but the former character is apt to be obscured by staining due to external causes, especially when the zoarium is attached to dead wood. The shape of the free statoblasts is too variable to be regarded as a good diagnostic character, but the fixed statoblasts, when they are to be found, are very characteristic in appearance. _P. javanica_ appears to be closely related to Allman's _P.

dumortieri_, with which stained zoaria are apt to be confused. The character of the ectocyst is, however, different, and the free part of the swim-ring is distinctly narrower at the sides of the free statoblasts. Dr. Kraepelin has been kind enough to send me one of the types.

TYPES in the Hamburg and Indian Museums.

GEOGRAPHICAL DISTRIBUTION.--Java, Penang, India. Indian localities are:--BENGAL, Calcutta; Berhampore, Murshidabad; R. Jharai, Siripur, Saran district, Tirhut: E. HIMALAYAS, Kurseong, Darjiling district (alt.

4,500 feet): MADRAS PRESIDENCY, ca.n.a.l near Srayikaad, Travancore. Mr. C.

W. Beebe has recently sent me a specimen taken by him in the Botanical Gardens at Penang.

BIOLOGY.--Very little is known about the biology of this species.

Kraepelin took it in Java on the leaves of water-lilies. It is not uncommon during the cold weather in the Calcutta Zoological Gardens on floating seeds and sticks and on the stems of bulrushes; in Travancore I took it in November on the submerged leaves of _Pandani_ growing at the edge of a ca.n.a.l of slightly brackish water. Mr. Hodgart, the collector of the Indian Museum, found it in the R. Jharai on the stems of water-plants at a time of flood in the "rains." In Calcutta it is often found entangled with _P. fruticosa_ and _P. emarginata_.

32. Plumatella diffusa, _Leidy_. (Plate IV, fig. 2.)

_Plumatella diffusa_, Leidy, P. Ac. Philad. v, p. 261 (1852).

_Plumatella diffusa_, Allman, Mon. Fresh-Water Polyzoa, p.

105 (1857).

_Plumatella diffusa_, Hyatt, Comm. Ess.e.x Inst. iv, pl. viii, figs. 11, 12 (1866).

_Plumatella diffusa_, _id._, _ibid._ v, p. 107, fig. 12 (1868).

_Plumatella repens_, Jullien, Bull. Soc. zool. France, x, fig. 37 (_lapsus_ for 73), p. 110 (1885).

_Plumatella diffusa_, _id._, _ibid._ figs. 155, 157, pp.

130, 131.

_Plumatella allmani_ var. _diffusa_, Annandale, Rec. Ind.

Mus. v, p. 49 (1910).

_Zoarium._ The zoarium often covers a considerable area on flat surfaces and is sometimes found crowded together on the stems of plants. In the latter case the arrangement of the main branches is distinctly radiate.

Upright branches occur rarely and never consist of more than three zooecia. The characteristic method of branching is best represented by the following diagram:--

[Ill.u.s.tration: Fig. 43.]

The part.i.tions are stout and numerous.

_Zooecia._ The great majority of the zooecia in each zoarium are distinctly L-shaped, the long limb being usually adherent. The vital organs of the polypide are contained in the vertical limb, while the horizontal one, in mature polyparia, is packed full of free statoblasts.

The zooecia are cylindrical and as a rule obscurely emarginate and furrowed. The ectocyst is stiff; it is never deeply pigmented but is usually of a transparent horn-colour at the base of each zooecium and colourless at the tip, the contrast between the two portions never being very strong. The basal portion is rough on the surface, the distal portion smooth.

_Statoblasts._ Free statoblasts are produced in very great profusion and fixed statoblasts are also to be found as a rule. The latter resemble those of _P. emarginata_. The free statoblasts are never very large or relatively broad, but they vary considerably as regards size and outline. The capsule is large, the sides convex outwards and the extremity more or less broadly rounded. The air-cells are unusually large and extend over a great part of the dorsal surface of the statoblast.

_Polypide._ The polypide is shorter and stouter than that of _P.

emarginata_ and as a rule has fewer tentacles.

The most characteristic feature of this species is the form of the zooecia, which differ greatly from those of any other Indian species but _P. allmani_. In the latter they are distinctly "keg-shaped" (_i. e._, constricted at the base and swollen in the middle), and the zoarium never spreads out over large surfaces in the way in which that of _P.

diffusa_ does.

TYPE--? in the Philadelphia Academy of Sciences.

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, Lah.o.r.e (_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, _Hanc.o.c.k_. (Plate IV, figs. 3, 3 _a_.)

_Plumatella allmani_, Hanc.o.c.k, 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 zooecia 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_.

GEOGRAPHICAL DISTRIBUTION.--_P. allmani_ is apparently a rare species to which there are few references in literature. It was originally described from England and is stated by Jullien to occur in France. I have found specimens only in the lake Bhim Tal (alt. 4,500 feet) in the W. Himalayas.

BIOLOGY.--The original specimens were found by Hanc.o.c.k on stones. My own were growing on the leaves of water-plants, usually on the under side.

When the zooecia were forced to stretch across from one leaflet to another they a.s.sumed the sinuous form characteristic of Allman's _P.

elegans_.

34. Plumatella tanganyikae, _Rousselet_.

_Plumatella tanganyikae_, Rousselet, Proc. Zool. Soc. London, 1907 (i), p. 252, pl. xiv, figs. 1-4.

_Plumatella bombayensis_, Annandale, Rec. Ind. Mus. ii, p.

169, figs. 1, 2 (1908).

_Plumatella bombayensis_, _id._, _ibid._ v, p. 51 (1910).