68 SUPPLEMENT TO THE CRAG MOLLUSCA. 
It has been sent to me by Messrs. Crowfoot and Dowson 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). 
Patupina ? exacraLis, S. Wood. Supplement, Tab. IV, fig. 14, a, 6., 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-marime 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. vvipyara 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 m 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 Jzéforime 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 of 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 Pal/udina at all, and I have assigned 
its name provisionally, and with doubt. 
