56 PALUDINID.E. 



are the largest of our freshwater Pectinibranchs. Lister 

 says he was indebted to Dr. Plot^ the historian^ for the 

 discovery that they were viviparous ; and he says that the 

 males are smaller than the females and their shells have 

 less-swollen whorls. They inhabit slow rivers^ ponds and 

 canals ; and one species lives within the influx of the tide 

 in the Thames. The epidermis of the last-formed whorl 

 in the young shell, when it leaves its mother, has three 

 transverse rows of recurved bristles, which in after- growth 

 are replaced by the coloured bands that encircle adult 

 shells, the formation of these bands, as well as of the 

 bristles, being caused by difierent organs which are suc- 

 cessively developed in the same part of the mantle. It 

 has been stated in that useful periodical 'The Zoologist' 

 (p. 7402) that our native Pahidince are not always vivi- 

 parous, and that a specimen of P. vivipara deposited in 

 an aquarium some eggs from which the fry were subse- 

 quently excluded. This was in the winter, and after the 

 Paludina had been kept for many months in a state of 

 confinement. It is hoped that further observations will 

 be made on this point, as the ovoviviparous character of 

 this genus constitutes one of the grounds of distinction 

 from the next genus, Bythinia. 



1. Paludina contec'ta*. Millet. 



Cyclosfoma contectum, Millet, Moll. Maine et Loire (1813), p. 5. P. Lis- 

 ten, F. & H. iii. p. 8, pi. Ixxi. f. 16. 



Body dark grey or brown, with yellow specks : head small, 

 but globular : snout prominent and bilobed : tentacles long and 

 widely spread out, blacldsh, with grey tips ; the right tentacle 

 of the male shorter and thicker at its point than the left : eyes 

 round and black : foot cloven or bilobed in front, and rounded 

 behind ; its tail or extremity nearly covered by the operculum 

 when the animal is crawling. 



* Covered (?". e. by the operculum). 



