23 



tant point. Sir Charles Lyell also informs me that a Dytiscus 

 has been caught with an Anmjlus (a fresh water shell like a 

 limpet) firmly adhering to it ; and a water beetle of the same 

 family, a Colymbetes, once flew on board the ' Beagle ' when 

 forty-five miles distant from the nearest land. How much 

 further it might have flown with a favouring gale no one 

 can tell." 



Where local conditions are favoiu-able for the support of 

 certain fresh water shells, it follows, from the remarks of the 

 learned naturalist, that there is no reason why isolated pools 

 throughout Tasmania may not be interstocked by means of 

 beetles and birds. The paucity or richness of local feed, 

 with difference in altitude, etc., will be sufiicient to effect 

 modifications from the parent type form such as we are 

 accustomed to see in Tasmania. I may, therefore, prior to 

 describing the new forms, sum up these few introductory 

 remarks by stating that, in my opinion, when the laws which, 

 according to our best authorities, determine the distribution 

 and relation of forms elsewhere, seem not to be able to 

 explain certain anomalies in the distribution of certain forms 

 in Tasmania, that the cause is more likely to be due to hasty 

 inference or the imperfection of material for the formation 

 of sound opinion than that the wide, well-considered, and 

 unanimous verdict of our best authorities should be mistaken. 

 I am not, however, aY>^are that there is anything anomalous 

 in the distribution of the fresh water shells of Tasmania ; 

 although I am persuaded that the meagre, isolated collections 

 in a new country should produce many forms which, becaiise 

 of the gaps, would seem very exceptional. 



JSTew Species. 

 (Sizes given in 3Iillimetres.) 

 GuNDLACHiA. (Pfeiffer.) 



Shell thin, obliquely conic ; apex inclined posteriorly ; base 

 closed for two-thirds by a flat horizontal plate ; aperture 

 semicircular. (WooclwarcV s Moll., p. 303.) 



GUNDLACHIA PeTTEKDI. 71. S. 



Shell minute, thin, pale horn, diaphanous, spirally oblong 

 in two distinct tiers, apex obliquely inclined posteriorly, con- 

 centrically striate and crossed by fine radiating liree, apical 

 tier more incrusted with confervoid matter, and appearing 

 partially and obliquely exserted upon the basal tier ; project- 

 ing portion of apical tier as well as one-third of the basal 

 one closed by a flat horizontal plate, all in the x^lane of the 

 original aperture of apical tier ; outer aperture broadly 

 ovate ; lip of basal tier continuous, although modified at 

 junction with apical tier ; inner aperture semicircular, and 



