152 BRITISH MOLLUSKS. 



Physa (Bidimus) fontinalis, Moquiu-Tandon (1855), Hist. Moll. vol. ii. 

 p. 451. f. 9 to 13. 



Sab. Throughout Europe. (On aquatic plants, both in stagnant and running 

 water.) 



Common as this sinistral water-snail is throughout Britain and 

 the whole of Europe, not only in tranquil ponds, ditches, and canals, 

 but also iu running brooks, it is not often seen with the mantle so 

 neatly developed as in our vignette of a living specimen crawling 

 on a leaf of Potamogeton, from a drawing obligingly contributed by 

 Mr. Berkeley. The animal has not been observed in this country 

 with the care it merits. Dr. Gray has given a woodcut of it, and 

 it is figured by Forbes and Hanley, but Mr. Jeffreys' figures of 

 this plentifully distributed mollusk are a copy of those of Moquin- 

 Tandon. More original observation of the animal of Physa fonti- 

 nalis is needed, for there are certainly two very distinct forms of 

 the species. The mantle is distinguished in a very characteristic 

 manner, by being reflected on either side of the shell in a digitate 

 lobe. In the short subglobose form figured by the above-named 

 authors, the lobes are quite lateral, but in the oblong form, with a 

 more produced spire represented in our vignette, it will be seen that 

 the right lobe is towards the front, and the left lobe is towards the 

 apes of the shell, the right lobe being always more digitate than the 

 left. Dr. Gray relates, in his edition of 1840 of Turton's ' Manual,' 

 that Mr. James Sowerby sent him a specimen of the long-spired 

 variety of Physa fontinalis under the name of Physa acuta ?, 

 which he received from Anglesey, and continued to breed in his 

 waterbutt. Mr. Sowerby named it acuta ?, as differing from the 

 common species in the following particulars : — " One of the lobes," 

 he says, " covers the columella and is five-parted, the other is tinned 

 upon the spire, and is three-parted." This interesting variety is the 

 mollusk of our vignette, but it is not the Physa acuta, which is quite 

 another species, a native of Central and Southern France, in which 

 the mantle is not reflected. 



The shell of Physa fontinalis is extremely thin and transparent, 

 and of a bright yellowish horny substance, moderately glossy. It 

 is composed of four whorls, always convoluted sinistrally, and has 

 a pyriforrnly ovate aperture, with the columella slightly callously 

 twisted. Its range of habitation appears to be very general through- 

 out Europe. Near London, it may be found abundantly in such 

 places as the marshy parts of Battersea and the Isle of Dogs. 



