(b) Actinozoa.
(4) Sagartia schilleriana, Stoliczka (1869).
S. schilleriana, Stoliczka, Journ. As. Soc. Beng. (2) xxxviii, p. 28, pls. x, xi (1869); Metridium schillerianum, Annandale, Rec. Ind. Mus. i, p. 47, pl. iii (1907).
This sea-anemone, which has only been found in the delta of the Ganges, offers a most remarkable instance of what appears to be rapid adaptation of a species to its environment. The typical form, which was described in 1869 by Stoliczka from specimens taken in tidal creeks and estuaries in the Gangetic area and in the ponds at Port Canning, is found attached to solid objects by its basal disk. The race (subsp. exul), however, that is now found in the same ponds has become elongate in form and has adopted a burrowing habit, apparently owing to the fact that the bottom of the ponds in which it lives is soft and muddy.
In addition to these four species a minute hydroid belonging to the order Gymnoblastea and now being described by Mr. J. Ritchie has been taken in the ponds at Port Canning. It is a very aberrant form.
Freshwater Cœlenterates other than Hydra.
Hydra is the only genus of cœlenterates as yet found in fresh water in India, but several others have been discovered in other countries. They are:—
(1) Cordylophora lacustris, Allman (1843).
Hincks, Hist. Brit. Hydr. Zooph. p. 16, pl. iii, fig. 2 (1868).
This is a branching hydroid that does not produce free medusæ. It forms bushy masses somewhat resembling those formed by a luxuriant growth of Plumatella fruticosa (pl. iii, fig. 1) in general appearance. C. lacustris is abundant in canals, rivers, and estuaries in many parts of Europe and has recently been found in the isolated salt lake Birket-el-Qurun in the Fayûm of Egypt.