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•which are of upper crag age, a single valve of Tellina baltliica. 
That this shell had accidentally found its way into this set of 
specimens is almost certain, for Messrs. Dowson and Crowfoot who 
have specially given their attention to the Aldeby deposits, have 
been on the look out for years for Tellina baltliica , and have never 
found any trace of it, and they are both of them far too careful 
observers, as well as too good conchologists, to have allowed such a 
find as this would have been, to have escaped their notice. I may 
perhaps, give an instance of the way in which such mistakes arise, 
which occurred a year or two since. Mr. Wood had sent to a 
gentleman at Blackpool, in Lancashire, a specimen of the character- 
istic crag shell Turrit ella imbricata to show the difference between 
the middle glacial sands of East Anglia, in which this shell 
plentifully occurs, and the middle sands of the West coast at 
Blackpool and elsewhere, in which it is absent, but in which the 
common English recent shell Turritella communis ( terebra ) is the 
prevailing form. A few months afterwards, Mr. Wood’s own 
specimen was returned to him mixed with a quantity of Blackpool 
shells, which were forwarded to him for identification. 
J)r. J. Gwyn Jeffreys states that Tellina baltliica is found in 
arctic seas, from Kamschatka and Behring Straits to the White Sea 
and Xovaya Zemlia. It inhabits the Baltic, whence its name, and 
is also found extending in its range from the north of France to 
the Mediterranean. Were it not that it is said to occur fossil in 
the pliocene beds of Sicily, we might suppose that it originated in 
arctic seas, and first visited our shores when the glacial cold 
commenced. However, as far as our own beds are concerned, it 
clearly marks, by its occurrence, or non-occurrence, the dividing 
line between the horizons of the crag, and glacial series. It first 
makes its appearance in the basement beds of the lower glacial 
deposits of the Cromer coast, being found also in the middle 
glacial sands, and the upper glacial beds of Dimlington and 
Bridlington. It occurs also in the boulder clay of the north-west 
of England, in the Moel Tryphaen and other mountain fossiliferous 
gravels, and in the Irish drifts. It is met with in all the post 
glacial deposits of Great Britain, being in East Anglia found in the 
March gravel, and the Nar valley brickearth, and it is invariably 
one of the most abundant forms met with. In the lower glacial 
beds it is often the case, that more than half the total number of 
