A=a zoœcium of Fredericella with the polypide extruded. B=the lophophore of Lophopus (tentacles removed) as seen obliquely from the right side. C=larva of Plumatella as seen in optical section. a=tentacles; b=velum; c=epistome; d=mouth; e=œsophagus; f=stomach; g=intestine; h=anus; j=retractor muscle; k=parieto-vaginal muscles; l=funiculus.

Two families may be recognized as constituting the division, viz., (a) the Fredericellidæ, which have a circular or oval lophophore and simple statoblast without a swim-ring, and (b) the Plumatellidæ, in which the lophophore is shaped like a horseshoe and some or all of the statoblasts are provided with a ring of air-spaces.

Family 1. FREDERICELLIDÆ.

Zoaria dendritic; zoœcia distinctly tubular, with the ectocyst well developed; statoblasts of one kind only, each surrounded by a chitinous ring devoid of air-spaces; polypides with the lophophore circular or oval when expanded.

The Fredericellidæ consist of a single genus (Fredericella) which includes several closely-allied forms and has a wide geographical distribution.

Genus FREDERICELLA, Gervais (1838).

This genus has the characters of the family. Its status has been much disputed, some authors regarding the shape of the lophophore as of great morphological importance, while Jullien believed that Fredericella was merely an abnormal or monstrous form of Plumatella. The latter belief was doubtless due to the fact that the zoaria of the two genera bear a very close external resemblance to one another and are sometimes found entangled together. The importance of the shape of the lophophore may, however, easily be exaggerated, for, as both Jullien and Goddard have pointed out, it assumes an emarginate form when retracted.

The best known species is the European and N. American F. sultana (Blumenbach), of which several varieties or phases have been described as distinct. This form is stated to occur also in S. Africa. F. australiensis, Goddard^[BC] from N. S. Wales is said to differ from this species in having an oval instead of a circular lophophore and in other small anatomical characters; but it is doubtful how far these characters are valid, for the lophophore appears to be capable of changing its shape to some slight extent and has been stated by Jullien to be habitually oval in specimens from France. F. cunningtoni, Rousselet^[BD] from Lake Tanganyika has stout zoœcia encrusted with relatively large sand-grains.

The zoaria of Fredericella are usually found attached to solid objects in shallow water, but a form described as F. duplessisi, Ford has been found at a depth of 40 fathoms embedded in mud at the bottom of the Lake of Geneva. F. cunningtoni was dredged from depths of about 10 and about 25 fathoms.

The statoblasts of this genus do not float and often germinate in the parent zoœcium after its polypides have died. They are produced in smaller numbers than is usually the case in other genera of the order. The polypides sometimes undergo a process of regeneration, but without the formation of brown bodies.

A=statoblast, × 120. B=outline of expanded lophophore and adjacent parts, × 75; a=anus, r=rectum. C=outline of zoarium on leaf of water-plant, × 3.

(A and B are from specimens from Igatpuri, C from specimen from Shasthancottah).

28. Fredericella indica, Annandale.

Zoarium. The zoarium is of delicate appearance and branches sparingly. It is often entirely recumbent but sometimes produces short, lax branches that consist of two or three zoœcia only.

Zoœcia. The zoœcia are very slender and almost cylindrical; they are slightly emarginate and furrowed, the keel in which the furrow runs being sometimes prominent. The external surface is minutely roughened and apparently soft, for small grains of sand and other débris cling to it, but never thickly. The ectocyst is practically colourless but not transparent.

Statoblasts. The statoblasts are variable in size and form but most commonly have a regular broad oval outline; sometimes they are kidney-shaped. The dorsal surface is covered with minute star-shaped prominences, which sometimes cover it almost uniformly and are sometimes more numerous in the centre than towards the periphery. The ventral surface is smooth.

Polypide. The lophophore bears about 20-25 tentacles, which are very slender and of moderate length; the velum at their base is narrow; as a rule the lophophore is accurately circular.

Type in the Indian Museum.

The most definite character in which this species differs from F. sultana and F. australiensis is the ornamentation of one surface of the statoblast, both surfaces of which are smooth in the two latter species. From F. cunningtoni, the statoblasts of which are unknown, it differs in having almost cylindrical instead of depressed zoœcia and in not having the zoœcia densely covered with sand-grains.

Geographical Distribution.—Western India (the Malabar Zone): Igatpuri Lake, W. Ghats (alt. ca. 2,000 feet), Bombay Presidency, and Shasthancottah Lake near Quilon, Travancore.

Biology.—In both the lakes in which the species has yet been found it was collected in November. The specimens obtained in Travancore were found to be undergoing a process of regeneration due at least partly to the fact that most of the polypides had perished and that statoblasts were germinating in the old zoœcia. Specimens from the Bombay Presidency, which were obtained a little later in the month, were in a more vigorous condition, although even they contained many young polypides that were not yet fully formed. It seems, therefore, not improbable that F. indica dies down at the beginning of the hot weather and is regenerated by the germination of its statoblasts at the beginning of the cold weather.

At Shasthancottah zoaria were found entangled with zoaria of a delicate form of Plumatella fruticosa to which they bore a very close external resemblance.

Family 2. PLUMATELLIDÆ.

Phylactolæmata which have horseshoe-shaped lophophores and a well-developed ectocyst not specialized to form an organ of progression. Some or all of the statoblasts are provided with a "swim-ring" consisting of symmetrically disposed, polygonal chitinous chambers containing air.

It is convenient to divide the Plumatellidæ as thus defined into subfamilies (the Plumatellinæ and the Lophopinæ), which may be defined as follows:—

Subfamily A. PLUMATELLINÆ.

Zoarium dendritic or linear, firmly fixed to extraneous objects; zoœcia tubular, not fused together to form a gelatinous mass.

Subfamily B. LOPHOPINÆ.

Zoarium forming a gelatinous mass in which the tubular nature of the zoœcia almost disappears, capable to a limited extent of progression along a smooth surface.

Both these subfamilies are represented in the Indian fauna, the Plumatellinæ by two of the three genera known to exist, and the Lophopinæ by two (or possibly three) of the four that have been described. The following key includes all the known genera, but the names of those that have not been recorded from India are enclosed in square brackets.

Key to the Genera of Plumatellidæ.

Subfamily A. PLUMATELLINÆ.

Of the two Indian genera of this subfamily, one (Plumatella) is almost universally distributed, while the other (Stolella) has only been found in the valley of the Ganges. The third genus of the subfamily (Stephanella) is only known from Japan.

It should be noted that zoaria of different species and genera of this subfamily are often found in close proximity to one another and to zoaria of Fredericella, and that the branches of the different species are sometimes entangled together in such a way that they appear, unless carefully separated, to belong to the same zoarium.

Genus 1. PLUMATELLA, Lamarck.

Zoarium dendritic, recumbent, erect, or partly recumbent and partly erect.

Zoœcia tubular, not confined in a gelatinous synœcium; the ectocyst usually horny.

Statoblasts often of two kinds, free and stationary, the latter without air-cells and as a rule adherent by one surface, the former provided with a well-developed ring of air-cells but without marginal processes, oval in form, never more than about 0.6 mm. in length.

Polypide with less than 65 tentacles.

A, of P. fruticosa (Calcutta); B, of P. emarginata (Calcutta); C, of P. javanica (Travancore); D, of P. diffusa (Sikhim); E, of P. allmani (Bhim Tal); F, of P. diffusa (Rajshahi, Bengal); G, G', of P. punctata (Calcutta); H, of P. diffusa (Sikhim), statoblast further enlarged: A=outline of capsule; B=limit of swim-ring on ventral surface; C=limit of swim-ring on dorsal surface. [The dark area represents the capsule of the statoblast.]

Certain forms of this genus are liable to become compacted together in such a way as to constitute solid masses consisting of elongate vertical zoœcia closely parallel to one another and sometimes agglutinated by means of a gummy substance. These forms were given by Lamarck in 1816 the name Alcyonella, and there has been much dispute as to whether they represent a distinct genus, distinct species, or merely varieties or phases of more typical forms. It appears to be the case that all species which produce vertical branches are liable to have these branches closely packed together and the individual zoœcia of which they are composed more or less greatly elongated. It is in this way that the form known to Allman as Alcyonella benedeni is produced from the typical Plumatella emarginata. Other forms go further and secrete a gummy substance that glues the upright zoœcia together and forces them to elongate themselves without branching. In these conditions the zoœcia become polygonal in cross-section. It is probable that such forms (e. g., Plumatella fungosa (Pallas)) should rank as distinct species, for the gummy secretion is present in great profusion even in young zoaria in which the zoœcia have not yet assumed a vertical position. No such form, however, has as yet been found in India, and in any case it is impossible to regard Alcyonella as a distinct genus.

Key to the Indian Species of Plumatella.

There has always been much difficulty in separating the species of Plumatella, and even now there is no general consensus of opinion as to the number that should be recognized. The difficulty, however, is much reduced if the following precautions are observed:—

(1) If the zoarium appears to be tangled, if the branches intertwine or overlap, or if the zoœcia are closely pressed together, the whole mass should be carefully dissected out. This is necessary not only because zoaria belonging to different species are sometimes found entangled together but also because it is often difficult to recognize the characteristic method of branching and shape of the zoœcia unless it is done.

(2) As large a part as possible of each zoarium should be examined, preferably with a binocular microscope, and allowance should be made for irregularities and abnormalities of all kinds. What must be observed is the rule rather than the exceptions.

(3) When the statoblasts are being examined, care must be taken that they lie flat and that their surface is parallel to that of the nose-piece of the microscope. If they are viewed obliquely it is impossible to see their true outlines and proportions.

(4) In order to see the relative proportions of the capsule and the swim-ring it is necessary that the statoblast should be rendered transparent. This is often difficult owing to the presence of air in the air-cells, but strong nitric acid applied judiciously will render it possible (p. 240).

In supervising the preparation of the plates that illustrate this genus I have impressed upon the artist the importance of representing what he saw rather than what he thought he ought to see, and the figures are very close copies of actual specimens. I have deliberately chosen for representation specimens of Plumatella preserved by the simple methods which are often the only ones that it is possible for a traveller to adopt, for the great majority of naturalists will probably have no opportunity of examining living specimens or specimens preserved by special methods, and the main object, I take it, of this series is to enable naturalists first to distinguish the species described and then to learn something of their habitat and habits.

Geographical Distribution.—Of the seven species included in this key five have been found in Europe (namely P. fruticosa, P. emarginata, P. diffusa, P. allmani, and P. punctata), while of these five all but P. allmani are known to occur in N. America also. P. javanica is apparently peculiar to the Oriental Region, while P. tanganyikæ has only been taken in Central Africa and in the Bombay Presidency.

Types.—Very few of the type-specimens of the older species of Plumatella are in existence. Allman's are neither in Edinburgh nor in London, and Mr. E. Leonard Gill, who has been kind enough to go through the Hancock Collection at Newcastle-on-Tyne, tells me that he cannot trace Hancock's. Those of the forms described by Kraepelin are in Hamburg and that of P. tanganyikæ in the British Museum, and there are schizotypes or paratypes of this species and of P. javanica in Calcutta. The types of Leidy's species were at one time in the collection of the Philadelphia Academy of Science.

Biology.—The zoaria of the species of Plumatella are found firmly attached to stones, bricks, logs of wood, sticks, floating seeds, the stems and roots of water-plants, and occasionally to the shells of molluscs such as Vivipara and Unio. Some species shun the light, but all are apparently confined to shallow water.

Various small oligochæte worms (e. g., Chætogaster spongillæ,^[BG] Nais obtusa, Nais elinguis, Slavina appendiculata and Pristina longiseta^[BH]), take shelter amongst them; dipterous larvæ of the genus Chironomus often build their protective tubes at the base of the zoaria, and the surface of the zoœcia commonly bears a more or less profuse growth of such protozoa as Vorticella and Epistylis. I have seen a worm of the genus Chætogaster devouring the tentacles of a polypide that had been accidentally injured, but as a rule the movements of the lophophore are too quick to permit attacks of the kind, and I know of no active enemy of the genus. The growth of sponges at the base of the zoaria probably chokes some species, but one form (F. fruticosa) is able to surmount this difficulty by elongating its zoœcia (p. 219). A small worm (Aulophorus tonkinensis) which is common in ponds in Burma and the east of India as far west as Lucknow, often builds the tube in which it lives mainly of the free statoblasts of this genus. It apparently makes no selection in so doing but merely gathers the commonest and lightest objects it can find, for small seeds and minute fragments of wood as well as sponge gemmules and statoblasts of other genera are also collected by it. I know of no better way of obtaining a general idea as to what sponges and phylactolæmata are present in a pond than to examine the tubes of Aulophorus tonkinensis.

I am indebted to Mr. F. H. Gravely, Assistant Superintendent in the Indian Museum, for an interesting note regarding the food of Plumatella. His observations, which were made in Northamptonshire, were unfortunately interrupted at a critical moment, but I have reproduced them with his consent in order that other observers may investigate the phenomena he saw. Mr. Gravely noted that a small green flagellate which was abundant in water in which Plumatella repens was growing luxuriantly, was swallowed by the polypides, and that if the polyparium was kept in a shallow dish of water, living flagellata of the same species congregated in a little pile under the anus of each polypide. His preparations show very clearly that the flagellates were passing through the alimentary canal without apparent change, but the method of preservation does not permit the retractile granules, which were present in large numbers in the cell-substance of the flagellates, to be displayed and it is possible that these granules had disappeared from those flagellates which are present in the recta of his specimens. It is clear, therefore, either that certain flagellates must pass through the alimentary canal of Plumatella unchanged, or that the polyzoon must have the power of absorbing the stored food material the flagellates contain without doing them any other injury.

The free statoblasts of Plumatella are as a rule set free before the cells they contain become differentiated, and float on the surface of the water for some time before they germinate; but occasionally a small polypide is formed inside the capsule while it is still in its parent zoœcium. I have, however, seen only one instance of this premature development, in a single statoblast contained in a small zoarium of P. fruticosa found in Lower Burma in March. The fixed statoblasts usually remain fixed to the support of the zoarium, even when their parent-zoœcium decays, and germinate in situ.

The larva (fig. 40 C, p. 207) that originates from the egg of Plumatella is a minute pear-shaped, bladder-like body covered externally with fine vibratile threads (cilia) and having a pore at the narrow end. At the period at which it is set free from the parent zoœcium it already contains a fully formed polypide or pair of polypides with the tentacles directed towards the narrow end. After a brief period of active life, during which it moves through the water by means of its cilia, it settles down on its broad end, which becomes adhesive; the polypide or pair of polypides is everted through the pore at the narrow end, the whole of this end is turned inside out, and a fresh polyparium is rapidly formed by budding.

29. Plumatella fruticosa, Allman. (Plate III, fig. 1; plate IV, fig. 4; plate V, fig. 1.)

Zoarium. The zoarium in the typical form has a loose appearance due to the fact that the branches are far apart and the ectocyst by no means rigid. When young the zoarium is adherent, but in well-grown polyparia vertical branches, often an inch or more in length, are freely produced. As a rule they have not the strength to stand upright if removed from the water. Branching is ordinarily lateral and as a rule occurs chiefly on one side of a main branch or trunk. In certain circumstances upright zoœcia are pressed together and reach a great length without branching, and in this form (P. coralloides, Allman) daughter-zoœcia are often produced at the tip of an elongated mother-zoœcium in fan-like formation. A depauperated form (P. stricta, Allman), occurs in which the vertical branches are absent or very short. In all forms internal partitions are numerous and stout.

Zoœcia. The zoœcia are cylindrical and bear a simple keel on their dorsal surface. They are never emarginate or furrowed. In the typical form their diameter is more than half a millimetre, and they are always of considerable length. The ectocyst is thin and never very rigid or deeply pigmented, the colour usually being an almost uniform pale pinkish brown and fading little towards the tip of the zoœcium.

Statoblasts. Both free and stationary statoblasts are formed, but the latter are rare and do not always adhere. They resemble the free statoblasts in general form but have a solid margin instead of a swim-ring and are often minutely serrated round the edge. The free statoblasts are at least considerably, sometimes very elongate; in all zoaria it is possible to find specimens that are more than twice as long as broad. The capsule is relatively large and resembles the swim-ring in outline, so that the free portion of the latter is not much narrower at the sides than at the ends. The sides are distinctly convex and the ends rounded; the swim-ring encroaches little on the surface of the capsule.

Polypide. The tentacles number between 40 and 50 and are not festooned at the base. The stomach is slender and elongate.

Type not in existence.

Systematic Remarks.—P. fruticosa is closely allied to P. repens (European and N. American) but always has much longer statoblasts. Three phases of the species may be distinguished as follows:—

A. (Forma typica). Zoœcia stout in form, not greatly elongate; free branches produced in profusion.

B. (P. stricta, Allman, P. repens, van Beneden). Zoœcia slender; free branches absent or consisting of two or three zoœcia only.

C. (P. coralloides, Allman). Vertical zoœcia pressed together and greatly elongated.

Indian specimens of the typical form agree well with German specimens labelled by Prof. Kraepelin P. princeps var. fruticosa, and specimens of the coralloides phase could hardly be distinguished from similar specimens from Scotland.

Geographical Distribution.—P. fruticosa is widely distributed in Europe and probably in N. America. I have seen Indian specimens from the Punjab (Lahore, Stephenson), from Bombay, from Travancore, from Calcutta and other places in the Ganges delta, from Rajshahi (Rampur Bhoolia) on the R. Ganges, from Kurseong in the E. Himalayas (alt. 4,500 feet), and from Kawkareik in Tenasserim. Statoblasts found on the surface of a pond near Simla in the W. Himalayas (alt. ca. 8,000 feet), probably belong to this species.

Biology.—Allman states that in England P. fruticosa is fond of still and slowly-running water. The typical form and the coralloides phase grow abundantly in the Calcutta tanks, the former often attaining an extraordinary luxuriance. I have found the var. stricta only in water in which there was reason to suspect a lack of minute life (and therefore of food), viz. in Shasthancottah Lake in Travancore, in a swamp in Lower Burma, and in a small jungle stream near the base of the Western Ghats in Travancore. The species is the only one that I have seen in running water in India, and the specimens obtained in the jungle stream in Travancore are the only specimens I have taken in these circumstances. P. fruticosa always grows near the surface or near the edge of water; it is found attached to the stems of bulrushes and other aquatic plants, to floating seeds and logs and (rarely) to stones and bricks. So far as my experience goes it is only found, at any rate in Calcutta, in the cold weather and does not make its appearance earlier than October.

The form Allman called P. coralloides was found by him, "attached to floating logs of wood, together with P. repens and Cordylophora lacustris, and generally immersed in masses of Spongilla fluviatilis." I have always found it immersed in sponges (S. lacustris, S. alba, S. carteri, and S. crassissima), except when the sponge in which it had been immersed had decayed. Indeed, the peculiar form it has assumed appears to be directly due to the pressure of the growing sponge exerted on the zoœcia, for it is often possible to find a zoarium that has been partially overgrown by a sponge and has retained its typical form so long as it was free but has assumed the coralloides form where immersed.^[BI] In Shasthancottah Lake, Travancore, I found specimens of the stricta phase embedded in the gelatinous mass formed by a social rotifer and to some extent assimilated to the coralloides form.

30. Plumatella emarginata, Allman. (Plate III, fig. 2; plate IV, figs. 1, 1 a.)

Zoarium. The zoarium often covers a considerable area on flat surfaces and is sometimes entirely recumbent. More usually, however, the younger part is vertical. In either case the branching is practically dichotomous, two young zoœcia arising almost simultaneously at the tip of a mother-zoœcium and diverging from one another at a small angle. When the zoarium becomes vertical, rigid branches of as much as an inch in length are sometimes produced in this way and, arising parallel to one another, are pressed together to form an almost solid mass (=Alcyonella benedeni, Allman). In such cases the basal zoœcium or at any rate the basal part of each upright branch is considerably elongated. In recumbent zoœcia the main branches often radiate outwards from a common centre.

Zoœcia. The zoœcia are of almost equal width throughout, slender, and moderately elongate when recumbent. Their ectocyst is stiff; they are emarginate at the tip and more or less distinctly furrowed on the dorsal surface, the keel in which the furrow runs not being prominent. The orifice is often on the dorsal surface even in upright branches. Each zoœcium is of a dark brown or almost black colour for the greater part of its length but has a conspicuous white tip which is extended down the dorsal surface in the form of a triangle, its limits being rather more extensive than and parallel to those of the emargination.

Statoblast. The majority of the free statoblasts are elongate and truncate or subtruncate at the extremities, the sides being as a rule straight and parallel. In every polyparium specimens will be found that are between twice and thrice as long as broad. The capsule is, however, relatively much broader than the swim-ring, often being nearly circular, and there is therefore at either end a considerable extent of free air-cells, while the extent of these cells at the sides of the capsule is small. The air-cells cover a considerable part of the dorsal surface of the capsule. Fixed statoblasts are usually found in old colonies, especially at the approach of the hot weather. They have an oval form and are surrounded by a membranous margin on which traces of reticulation can often be detected. As a rule statoblasts of both types are produced in considerable but not in excessive numbers.

Polypide. There are about 40 tentacles, the velum at the base of which extends upwards for a considerable distance without being festooned. The stomach is elongate and slender and narrowly rounded at the base.

The method of branching, the coloration of the zoœcia and the form of the free statoblast are all characteristic. Luxuriant or closely compressed zoaria of P. diffusa often bear a superficial resemblance to those of P. emarginata, but the resemblance disappears if they are carefully dissected out. Indian specimens of P. emarginata agree closely with European ones.

Geographical Distribution.—P. emarginata is a common species in Europe, N. America, and southern Asia and probably also occurs in Africa and Australia. I have examined specimens from Calcutta, Rangoon, and Mandalay in Indian territory, and also from Jalor in the Patani States (Malay Peninsula) and the Talé Noi, Lakon Sitamarat, Lower Siam. Gemmules found by Apstein (Zool. Jahrb. (Syst.) xxv, 1907, p. 201) in plankton from the Colombo lake may belong to this species or to any of the others included by Kraepelin in his P. princeps.

Biology.—In Ireland Allan found P. emarginata in streams and rivulets, but it also occurs in European lakes. In India I have only found it in ponds. It prefers to adhere to the surface of stones or bricks, but when these are not available is found on the stems of water-plants. In the latter position the form called Alcyonella benedeni by Allman is usually produced, owing to the fact that the upright branches are crowded together through lack of space, very much in the same way (although owing to a different cause) as those of P. fruticosa are crowded together in the coralloides phase, to which the benedeni phase of P. emarginata is in many respects analogous.

Although it is essentially a cold-weather species in Calcutta, P. emarginata is sometimes found in a living condition during the "rains." Zoaria examined at this season, however, contains few living polypides, the majority of the zoœcia having rotted away and left fixed statoblasts only to mark their former position.

31. Plumatella javanica, Kraepelin.

This species is related to P. emarginata, from which it may be distinguished by the following characters:— Zoarium. The zoarium is always entirely recumbent and branches sparingly; its method of branching does not approach the dichotomous type but is lateral and irregular. Linear series of zoœcia without lateral branches are often formed.

Zoœcia. The zoœcia are slender and often very long; they are strongly emarginate and furrowed, and the keel that contains the furrow is conspicuous. The ectocyst is hyaline and as a rule absolutely colourless.

Statoblasts. The free statoblasts are variable in length, sometimes distinctly elongate, sometimes elongate only to a moderate degree; they are rounded at the extremities and have the sides slightly or distinctly convex outwards. The capsule is relatively large, and the free portion of the swim-ring is not much broader at the ends than at the sides. The fixed statoblasts are elongate and surrounded by an irregularly shaped chitinous membrane, which is often of considerable extent. The whole of the dorsal surface is covered with what appear to be rudimentary air-spaces some of which even contain air.

The transparent glassy 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, canal 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 canal 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.)