68 



of Liilioglypliv.s. But since LitliogJyiyJius (Muhlfeldt) and 

 Hydrohia are botli maintained, though probably under con- 

 ditions different from those originally contemplated by these 

 authors, it remains to be seen under which genus we are to 

 place the small freshwater shells of Tasmania which I re- 

 garded as Bythinia. It seems to me that in this matter our 

 safest and best plan is to follow the arrangement of Messrs. 

 Adams, because that is the one which is generally adopted, 

 and that seems to be most natural and most in accord with 

 the claims of priority in the nomenclature. I admit, how- 

 ever, that where the claims are so various and on such dif- 

 ferent grounds, and where we do not follow the authors' 

 definitions, there is too much confusion for any one to decide 

 on a generic name from priority alone. 



According to the authors of the Genera of Recent Mollusccif 

 Litlioglyplius is placed in the family of Littorinidce, and is 

 thus defined : — Shell semi-globose, thick, solid ; spire short, 

 obtuse ; whorls few, smooth ; aperture large, ovate, entire ; 

 peristome continuous ; inner lip callous ; outer lip simple ; 

 umbilicus rimate. They add that the typical species of this 

 genus is from the river Danube ; a few other species are 

 inhabitants of the fresh waters of South America, and have 

 been described by Mons. D'Orbigny under the name of 

 Paladestrina.^ 



It is very cleo^r that this definition will not corresj^ond 

 with those of Tasmania with which we are now^ dealing. 



Hydrohia, on the other hand, is placed by the same authors 

 in the family Bissoidcc, and is defined thus : — Operculigerous 

 lobe simple ; operculum sub-spiral ; shell elongately conical, 

 thin, smooth, covered with an olivaceous ej^idermis ; axis 

 imperforate ; apertiu^e oval ; peritreme continuous.; outer lip 

 simple, acute. Syn. Leachia (Risso), not Lesueur or Johnst. 

 Liftorinella (Braun). Example — H. iilvcT^ (Pennant, loc. cit., 

 p. 335). I may add that the animal has the eyes at the base 

 of the tentcicles, the foot is broadly wedge-shaped, the broad 

 end under the muzzle. Messrs. Adams say that the tentacles 

 are subulate. There are 30 species known — one from New 

 Zealand, described by Gray (H. Zelandice), two described 

 by Grould (if. tadia and H. egena) and two by Mons. P. 

 Fischer {H. Saleana and H. Cumingiana). There is one 

 described from Western Australia named H. Preissii (Phil). 



There can be no doubt that the most of our shells belong 

 to this genus, as far as the shells can guide us ; but further 

 observations are rec[uired upon the animal. There is only 

 one genus with which it can be confounded, and that is 



^ Genera Becent MoUnsca, vol. 1, p. 320. 



