68 SUPPLEMENT TO THE CRAG MOLLUSCA. 



It has been sent to me by Messrs. Crowfoot and Dovvson from the Fluvio-marine 

 deposit of Yarn Hill, near Potter's Bridge, Southwold, and Mr. Bell gives it from the 

 Red Crag of Walton ('Ann. and Mag.,' September, 1870). 



Paludina ? glacialis, S. Wood. Supplement, Tab. IV, fig. 14, a, 5,, Tab. VII, fig. 25. 



Localities. Chillesford Bed, Coltishall. Lower Glacial, Belaugh and Rackheath. 

 Middle Glacial, Hopton. 



Several specimens of this shell have occurred in the pebbly sands of Belaugh and 

 Rackheath, and recently another was put into my hands by H. Norton, Esq., of Norwich, 

 from the shell bed beneath the Chillesford Clay, at Coltishall. 



The volutions in this shell, which I have referred to the genus Paludina, are 

 flat, or rather inclined to be concave externally ; the mouth is subcircular, and the inner 

 lip slightly extends over a small umbilicus ; the shell is by no means thin, and the apex 

 is very much flattened. The lower glacial sands in which this shell has occurred, as 

 well as the Chillesford Sand at Coltishall, are of Fluvio-marine origin ; and in them, in 

 actual association with this Paludina glacialis, specimens of P. vivipara occur, none of 

 them presenting any sign of departure from their normal form ; and I have seen nothing 

 which by connecting this shell with P. vivipara would justify the idea that it was a 

 variety of that shell. Moreover, it is difficult to conceive that any species of Paludina 

 could thus assume so very distinct a form (which is shown to be common to several 

 individuals) while living in association with the unaltered normal form of that shell. 



The Middle Glacial specimen in Tab. VII differs in being more flattened, and it is 

 from a formation which has not only afforded no indication of Fluvio-marine conditions, 

 but whose physical relations indicate it to have been accumulated under several hundred 

 feet of sea depth. The presence however, in abundance of Liltorince in the Middle 

 Glacial sands, renders it probable that some at least of the shells of those sands lived near 

 a shore, and were transported by currents to the place where we now find them, so that 

 the shell may in this way have been a denizen of an estuary or of a river, which was 

 carried into a purely marine and deep-water area. Assuming this, and that it is really 

 the young oi glacialis, the shell must have undergone a change from its original form in 

 the interval between the commencement of the Lower Glacial formation, where we get the 

 shell at Belaugh and Rackheath, and the accumulation of the Middle Glacial deposit. It 

 is quite possible, however, that the shell may be no Paludina at all, and I have assigned 

 its name provisionally, and with doubt. 



