176 Mr. W. T. Blanford on the Animal and 



which occasionally shows a trace of spiral structure at the 

 lower part of the left side ; additions are made to the left side 

 and the apex, so that the strias seen running from the nucleus 

 are bent over in an open curve above. Inside, at the nucleus, 

 there is a projection of considerable size, with a blunt termi- 

 nation, which increases the resemblance, already existing in 

 other characters, to the opercula of the smaller Neritince. 



" The animal is short, the foot rounded off and broader in 

 front ; the head separated from it and but slightly emarginate 

 and broad when at rest, but when the animal is creeping it is 

 stretched out somewhat like a proboscis. On the top of the 

 head are two short triangular tentacles, bearing large black 

 eyes on the upper bases. 



" The operculum is fastened on the hinder portion of the 

 foot, as in Paludina." 



The accompanying figures are not good ; and if a specimen 

 in my possession be authentic (as I have every reason to believe 

 it is), they convey a very inaccurate idea of the form of the 

 shell and its colour, which is of the same peculiar amber tint 

 as in Georissa, and resembles that of some of the more deeply 

 coloured Succinece. I am therefore induced to doubt if the 

 representations of the operculum* are exact. The only im- 

 portant distinction shown by the latter from that of Georissa 

 is in the striation, which, as described, shows a different mode 

 of increase in the operculum. The internal process is very 

 nearly the same. 



So far as the shell is concerned, there is evidently no dis- 

 tinction of any consequence between the two types ; and the 

 differences presented by the operculum are at the most sub- 

 generic ; but the distinctions shown by the animals are of some 

 importance. They are, briefly (if Kuster's figures and descrip- 

 tion are trustworthy, and I can certainly see no reason why 

 any shortcomings in the former should imply inaccuracy in 

 the latter) : — that, to use Pfeiffer's terms, Hydrocena is opisoph- 

 thalmate, while Georissa is ectophthalmate, the former having 

 the eyes above the base of the tentacles, the latter at the side; 

 and also that in Hydrocena the operculum is carried on the 

 end of the foot, at some distance from the aperture — in Georissa 

 close to the aperture, the foot being only extended a very short 

 distance behind, and being generally shorter and rounder in 

 the latter genus. 



Were this the only distinction, I should be much disposed, 

 taking into consideration the marked similarity of the shell 



* I have endeavoured ^o extract the operculum in the only specimen 

 of Hydrocena eattaro'ensis which I possess ; hut it is too deeply inserted 

 iu the shell to be removed without breaking the aperture. 



