BRITISH OYSTERS : OLD AND NEW. 185 
shells are plentiful and usually in fine condition, as in the case of 
other genera. 
M. Sars (Edin. New Phil. Mag. 1863) records the oyster from 
the Glacial Beds of S. Norway, at Ivellebo, in Rakkestaat, at 
300—440' elevation. In the Christiania region, Brgger makes 
the great Oyster banks the earliest post-glacial deposits ; 
these and the succeeding Tapes banks are possibly 
the equivalent of our Irish Estuarine Clays, as well as those 
of the Nar Valley and Grangemouth. Oyen gives Trondjhem 
for its farthest appearance northwards in a post-glacial deposit, 
where specimens are found 105 mm. long. Thick masses of 
shells abound on the shores of the Cattegat, where the oyster 
flourished during Neolithic times, as the hundreds of shell- 
heaps testify, some of them being banks 1,000 feet in length, 
by 80 to 150 feet in breadth. The shells are of the usual size, 
but, owing to the influx of fresh water from the Baltic during 
the Ancylus -sea period, died out, as the mollusc cannot exist 
in water containing less than 16 or -17 parts in 1,000 of saline 
matter. (Sir H. Howorth, Geol. Mag. 1905, p. 461). Forchammer 
[Trans. Geol. Soc., vol. v. (1837-40) p. 159] reports that 
in Holstein at 150 feet above sea level a bed of pebbles with 
Cardium edule, Buccinum undatum and Ostrea edulis occurred, 
the oysters being much smaller than those now living on the 
Coast. 
Thanks to the courtesy of Dr. Odhner of Stockholm, Dr. 
Oyen, of Christiania, and Prof. Ravn, of Copenhagen, I am 
now in possession of a fair series of oysters from Norway, Sweden 
and Denmark, including Uddevalla, Bohuslan (recent and fossil), 
the Danish Kjokkenmoddings, and the Limfiord, in the North 
of Jutland. The Uddevalla shell in some respects approaches 
the Irish estuarine form in the incurving of the upper valve, but 
it has much more exuberant foliation or fluting on the lower 
valve where the growth-lines intersect the costae, and the valves 
are slighter in texture with more delicate laminar growth at 
the margin of the shell. The Uddevalla shell has the laminae 
of the top valve set very close, not projecting beyond the plain 
margins ; lower valve with well-developed costae, rising with 
hollow ridges where intersected by the annual shoots or growth- 
marks. The midden-heap shells approximate to the Celtica 
group in the strength of the costae. One type of the recent 
