60 PALUDINID^ 



these mollusks inhabit deeper water than others of the 

 same family, such is not the case. They generally fre- 

 quent small streams, canals, shallow ponds and ditches. 

 They lay their eggs in three long rows on stones, as well 

 as on the stalks and leaves of water-plants. 



1. Bythinia tentacula'ta *, Linne. 



Helix tentaculata, Linn. Syst. Nat. ed. xii. p. 1249. Bithinia tcntaculafa, 

 F. & H. iii. p. 14, pi. 1^. f. 5, 6, and (animal) pi. H. H. f. 3. 



Body dark bro^Ti or almost black above, dirty grey beneath, 

 covered with small and irregular specks of yellow : head small 

 and semioval : snout long and deeply cleft in front : tentacles 

 very long and slender, greatly diverging : eyes large, oval, and 

 black : foot much broader than the snout, rounded in front, 

 with a blunt and rounded tail which is half concealed by the 

 operculum when the animal is crawling. 



Shell subconical or oval, rather sohd and glossy, nearly 

 opaque, of an amber colour, with often more or less of a brown- 

 ish tint, very finely and closely striate in a spiral direction and 

 crossed transversely by the marks of growth ; the spii'al striae 

 are sometimes confluent and form white lines : epidermis very 

 thin : whorls 6, convex ; the last exceeding one-half of the 

 shell, and the rest diminishing in proportion and ending in 

 rather a sharp point : suture rather oblique and deep. : mouth 

 oval, angular above : outer lip thick, and sometimes strength- 

 ened by a white, rather strong, internal rib, which when re- 

 peated gives the shell a slightly varicose appearance ; this hp 

 is very little reflected : inner Up united to the columella, but 

 forming with the other hp a complete peristome : umhilical 

 chink small and narrow : operculum obhquely oval, very thick, 

 angular at the top, compressed or indented in the middle of 

 the upper half; it is marked with exquisitely fine concentric 

 stria} and a few coarser ridges, denoting the marks of periodical 

 increase, which form raised platforms or layers, the smallest 

 or first-formed being uppermost. L. 0-5. B. 0-25. 



Var. 1. ventricosa. Shell white: whorls more swollen. 

 Paludina ventricosa, Menke. 



Var. 2. decoUata. Upper whorls wanting in half-grown and 



* Having tentaclea. 



