P A L U J) 1 N A 



I'late I. 



Geiuis PALUDINA, Lamarck. 



Testa ovato-conica, flerumque imbilicata, interdum mnbilico 

 fere claiino, mifractibus quinque ad sex, lavii/ads aat 

 spiraliter fiiiuciilads, epidenuide fiisco vel oVwaceo- 

 vlrente, interdiim c'diatd, mdidis ; aperturd sapimme 

 fyriformi-rotundald, labro simplici. Opercitlum cor- 

 veum, concentricitm, nucleo sublaterali. 



Shell ovately conical, generally umbilicated, sometimes 

 with the umbilicus almost closed, whorls hve to six, 

 smooth or spirally corded, covered with a brown or 

 olive-green epidermis, which is sometinn's ciliated ; 

 aperture most fre(|ueutly jjyriforndy rounded, lip 

 simple. Operculum horny, concentric, with the 

 nucleus sublateral. 



In studying the genus Paludina it is necessary to give 

 especial attention to the animal. Dr. Gray noticed, as 

 long back as 1831, in a paper in the ' London Medical Re- 

 pository,' that two out of the four moUusks of our own 

 streams hitherto regarded as Faludma, were distinguished 

 by characters peculiarly their own, ami the distinction has 

 now been established in a very niunerous scries of foreign 

 species. Bitliyuia, the genus proposed for their reception, 

 is more numerous in species than Paludina. The animal 

 differs, as we shall presently see, in being oviparous, in 

 having the eyes sessile, the mantle comparatively simple, 

 and the tentacles slender anil thread-like, while the shells 

 are uniformly smaller. 



The PuludincB are ovo-viviparous, the eggs being hatched 

 in the ovary, whence, at the end of about two months, the 

 young are ejected, three or four at a time, alive. The 

 animal has a largely dilated foot, broad in front and at- 

 tenuately rounded behiiul ; the head is produced into a 

 proboscis, and the tentacles, unlike those of Bithynia, are 

 rather stout and cylindrical, with the eyes raised on shoi't 

 conjoined stalks. This modification in the position of the 

 eyes, is apparently designed to make room for an organ at 

 the outer base of the right tentacle, used for conveying 

 water to the branchial chamber. It is in the form of a 

 tubular lobe, and on the left side of the neck there is a 

 corresponding lobe, to which no particular use is assigned. 

 In the large Ampidlar'ue of the tropics, affecting situations 

 where the water is more liable to be dried up, the animal 

 is provided with a double system of respiration, having, 

 in addition to the branchial chamber on the right side, 

 a pulmonary chamber on the left side. The dormant lobe 

 of Paludina is then developed into an elongated siphonic 



tube, for the passage to this chamber of the air. In most 

 of the marine water-breathing Cephals, the siphonic lobes, 

 which appear in such a rudimentary form in Paludina, are 

 combined into a conspicuous central tube adapted to the 

 same use, ami the shell is cither notched in front for its 

 reception, as in Buccinnm., or extended into a long canal 

 for its special protection, as in Mnrex. 



The general distribution of Paludina over the globe, 

 does not range with that of the inoperculated freshwatei- 

 genera Planorbis, Lymnaa, or Physa. We have no record 

 of its existence in South Australia, New Zealand, or Poly- 

 nesia ; nor does it appear in the West Indies or South 

 America. About seventy 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 thirteen species, embracing several very 

 characteristic varieties of form, sculpture, and painting. 

 In some, the shells are conspicuously keeled, in others they 

 are prettily banded, but greeu or olive-green is in all the 

 predominant ground-colour. The Philippine Island rivers 

 contribute only half-a-do/.en comparatively insignificant 

 species of Paludina, their place being occupied to a great 

 extent by Melania, remarkable for the size and exquisitely 

 acuminate proportions of their shells ; and in Ceylon the 

 rapids, chiefiy those flowing from Adam's Peak, are in- 

 habited by a very characteristic group having peculiarly 

 globose shells, Tanalia and Paludoinus. 



The remainder of the Old World Paludina, so far as 

 they are at present known, are six from Borneo, Java, 

 Celebes, six from Burmali and Siam (in which latter 

 country the land and freshwater mollnsks all present 

 strikingly new specific forms), and nine from more northern 

 latitudes, of which two are European, two Siberian, and 

 five Japanese. Temperature, which has so marked an 

 infiuence in the development of molluscan life among the 

 land snaOs, as may be seen by comparing the West African 

 and Philippine Helices and Bnlimi with the European, or 

 those of Bolivia and Venezuela with the North American, 

 has comparatively little influence among the water snails. 

 We have no such large PJiysce in Britain as inhabit Australia 

 and the West Indies, but in Lymnaa stagnalis, which 

 ranges eastward and northward to Siberia, we have the 

 largest species known of that genus ; and we have also in 

 Britain the largest known Planorbis. It is the same with 

 Paludina in Russian Asia. The largest variety of the P. 

 (jigantea of Bengal is exceeded in size by P. Ussuriensis, a 



April, 1863. 



