31. Plumatella javanica, Kraepelin.
Plumatella javanica, Kraepelin, Mitt. Nat. Mus. Hamb. xxiii, p. 143, figs. 1-3 (1903). Plumatella emarginata var. javanica, Loppens, Ann. Biol. lacustre, iii, p. 162 (1908). Plumatella javanica, Annandale, Rec. Ind. Mus. v, p. 50 (1910). Plumatella allmani var. dumortieri, id. (partim) (nec Allman), ibid. p. 49.
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.)