468 Recent freshwater Mollusca. 



ART. XL. — ENUMERATION OF THE RECENT FRESHWATER MOL- 

 LUSCA WHICH ARE COMMON TO NORTH AMERICA AND EUROPE ; 

 WITH OBSERVATIONS ON SPECIES AND THEIR DISTRIBUTION. By 

 S. S. Haldemai?, Professor of Zoology in the Franklin Institute, Philadelphia. 



1. Paludina vivipara, Lin. 



2. P. fasciata, Midi, achatina, Lam. 



3. Physa hypnorum, Lin. elongata, Say. 



4. Limnea palustris, Mull, elodes, Say. 

 L. stagnalis ? Lin. jugularis, Say, 

 L. truncatulus, Midler, 



5. Planorbis albus " 

 P. nitidus ? <^ 



6. Cyclas calyculata, Draparnaud. 



7. Pisidium appendiculatum, Leach. 

 P. amnicum ? Midler. 



8. Alasmodon margaritiferus, Lin. 



Mr. James Sowerby catalogues several other European 

 freshwater species as found by Dr. Richardson, in the upper 

 Canadian lakes ; but I am unwilling to adopt these deter- 

 minations on the present occasion, except that of Pisidium 

 appendiculatum, which cannot well be mistaken for another 

 species, and which is mentioned as occurring from Lake 

 Superior to Saskatchewan. 



It is difficult to determine the percentage of species com- 

 mon to the two continents, and tlie result will vary according 

 to the point in which the facts are viewed. Paludina vivipara 

 and fasciata, for example, appear to be the only European 

 members of the restricted genus, and arc found here, where 

 the species arc more multiplied. We count Unionidos and 

 Melaniadaj by the hundred, whilst the former family has but 

 few species, and the latter but two recorded recent Melania 

 in Europe.* Under these circumstances, I have deemed it 



* I doubt much whether these will not be found, upon a closer scrutiny, to belong 

 to Melanopsis, which appears to be as essentially a European — as Melania is an 



