342 DR. N. ANNANDALE ON 



Switzerland and von Ledenfeld's 1 H. hexadinella from Queensland (which is possibly 

 a distinct form), the following ' ' key ' ' will at any rate afford an approximation to the 

 true state of the genus, so far as its forms have been investigated. It is possible that 

 detailed investigation of the southern forms will add considerably to their number. 



A. Chlorophyll-green. 

 I. Hermaphrodite — 



{a) Tentacles shorter than body : eggs spherical, with reticulated surface. . 



H. viridis. 



B. Olive-Green, Grey, Brown, Orangk, Cream, or White. 



I. Hermaphrodite — 



(a) Tentacles not longer than body ; eggs spherical, set with coarse spines 



which are expanded or bifid at the tips H. grisea. 



(b) Tentacles much longer than body ; eggs depressed, with short, simple 



spines on the upper part, smooth below H. fusca. 



II. Dicecious ; tentacles much longer than body — 



(a) Eggs subspherical, with short, simple projections on the surface ; gonads 

 produced near the aboral pole H. dicecia. 



(!>) Normal eggs subspherical, set with fine spines which are bifid or 

 expanded at the tip ; gonads confined to the upper part of 

 the body H. orientalis. 



H. orientalis agrees with H. dicecia in several respects, but differs from it not only in 

 the characters noted in the key but also (i) in not having the tentacles expanded at the 

 tips ; (2) in having only from 5-6 tentacles (at any rate in Calcutta) ; (3) in producing, 

 under certain conditions, thin-shelled eggs. Breeding females could be distinguished 

 from egg-bearing individuals of H. grisea by the relative length of the expanded tentacles. 



Distribution of the genus in Asia. 



Extremely little is known on this point. In the latest summary of the distribu- 

 tion of the genus (Hartlaub, 1905) no mention is made of Southern Asia ; but von 

 Daday ; has recorded a species from Turkestan (and also from Siberia), and Richard 4 

 one from Tonquin. Mr. E. E. Green and Dr. A. Willey tell me that they have taken 

 Hydra in Ceylon ; while I have seen several specimens in an aquarium at Penang. 



In India, I found numerous specimens of a polyp probably identical with H. 

 orientalis attached to the roots of Duckweed at Pusa (North Bihar) in November ; but 

 failed to ascertain the occurrence of any form either at Pamben, on Rameswarem 

 Island (Palk's Straits), in August, or at Port Canning, in Lower Bengal, in January. 

 The majority of the pools investigated at both these places were more or less brackish ; 



1 Zool. Jahrb., II, 1887, p. 96, pi VI., figs., 13, 14. 3 Zool. Jahrb. Syst., XIX, 1904, p. 480. 



2 Zool. Jahrb., Suppl. VI, 1905, p. 517. * Mem. Soc. Zool. France, VII, 1894, p. 237. 



