FAMILY PERISTOMATA. 193 



range with that of the inoperculated freshwater genera Planorbis, 

 Lymncea, or Physa. We have no record of its existence in the 

 waters of Australia, New Zealand, or Polynesia ; nor does it ap- 

 pear in the West Indies or South America. About sixty species 

 are known, of which rather more than two-thirds belong to the 

 Eastern Hemisphere, and the remainder to North America. India 

 and China, the chief area of habitation of this genus in the Old 

 World, contribute about fifteen species, embracing several very 

 characteristic varieties of form, scidpture, and painting. In some, 

 the shells are conspicuously keeled, in others they are prettily 

 banded, but green or olive-green is in all the predominant ground 

 colour. The Philippine Island rivers contribute only half-a-dozen 

 comparatively insignificant species of Paludina, their place being 

 occupied to a great extent by Melanice, remarkable for the size and 

 exquisitely acuminate proportions of their shells ; and in Ceylon 

 the rapids, chiefly those flowing from Adam's Peak, are inhabited 

 by a very characteristic group having peculiarly globose shells, 

 Tanalia and Paludomus. 



The remainder of the Old World Paludince, so far as they are at 

 present known, are three from Borneo and Celebes, three from 

 Burniah and Siam, (in which latter country the land and freshwater 

 mollusks all present strikingly new specific forms,) and six from 

 more northern latitudes, of which two are European, two Siberian, 

 and two Japanese. Temperature, which has so marked an in- 

 fluence in the development of molluscan life among the land snails, 

 as may be seen by comparing the West African and Philippine 

 Helices and Eulimi with the European, or those of Bolivia and 

 Venezuela with the North American, has comparatively little in- 

 fluence among the water snails. We have no such large Physa in 

 Britain as inhabit AustraHa and the West Indies, but in Lymncea 

 stagnalis, which ranges eastward and northward to Siberia, we 

 have the largest species known of that genus. It is the same with 

 Paludina. The largest variety of the P. gigantea of Bengal is 

 exceeded in size by P. Ussuriensis, a species collected by Gerstfeldt 

 at the mouth of the Ussuri, a tributary of the Amoor, in Siberia, 

 which is in the isothermal latitude of Lapland, little south of the 

 line of permanent ground frost. The European Paludina vivipara, 

 at least a fight inflated form of similar structure and colour referred 

 to that species, appears in North America, but the Paludince of that 

 continent consist of sixteen species, chiefly of a peculiarly solid 

 type, forming the genus Melantho of Bowditch. 



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