﻿BIVALVIA. 



119 



Anodonta cygnea, Linn. Crag Moll., vol. ii, p. 102, Tab. II, fig. 10. 



This is also an abundant shell at Grays, and by no means scarce at Clacton, but 

 from extreme fragility specimens are difficult to obtain. I have also found in the bed at 

 Runton (C of Sect. Ill of the map sheet) the variety anatina or paludosa, ' Turt. Brit. 

 Biv.,' p. 240, Tab. 15, fig. 6, in which the dorsal and ventral margins are nearly parallel. 

 My specimen from Runton measures nearly five inches in length. 



TJjiio margaritifer is given by Mr. Prestwich in the 'Quart Journ. Geol. Soc.,' vol. 

 xxvii, p. 467, as a species from near Runton Gap on the Norfolk Coast, but this appears 

 to be an error, as pointed out by Mr. A. Bell in ' Geol. Mag.,' vol. ix, p. 214. I do not 

 know this shell as a British fossil. 



Corbicdla fluminalis, Midler. Crag. Moll., vol. ii ; p. 104, Tab. XI, fig. 15, as Cyrena 



consobrina. 



Localities. Red Crag, Waldringfield (A. Bell). Pluvio-marine Crag. Thorpe, near 

 Aldbro (S. Wood). Dunwich (Crowfoot). Bramerton and Postwick (Woodward). 

 Bulchamp (Dowson). Lower Glacial, Belaugh (Harmer). Post Glacial, Bramwell near 

 Cambridge (Bell). Kelsea Hill, Gedgrave near Orford, Stutton-on-Stour, Grays, and 

 Clacton (Fisher). 



This shell (like several European freshwater bivalves) has a great number of 

 synonyms, 1 and it is an important species as concerns the post glacial sequence of deposits. 

 It is somewhat variable, but not more so than other of our freshwater inhabitants. It 

 has been said that freshwater shells vary more than marine, but I have never seen 

 greater variation among them than is exhibited by the varieties and distortions shown bv 

 fossil specimens of Trophon antiquus and Littorina littorea. 



The Red Crag appears to be the oldest deposit in which Corbieula fluminalis has been 

 met with in this country. The specimens of this species mentioned by me as having 

 been found on the top of the Cor. Crag at Gedgrave (' Crag Moll.,' vol. ii, p. 105) belong 

 to what is probably one of the older Post Glacial deposits, into which some of the Cor- 

 Crag fossils have been washed. It appears to have lived in Britain before the very severe 

 conditions of the Glacial Period had set in, and we find it again an inhabitant of our 

 waters in deposits more recent than those of that epoch, but all the specimens that I have 

 seen from the beds of Crag age, as well as the solitary specimen I have seen from the 

 Lower Glacial sands at Belaugh, are small ; the largest of them scarcely more than half 



1 This species, including the fossil in Europe and the recent shell from the Nile and China, has had 

 given to it five generic and sixteen specific names. Mr. Gregory (' Geol. Mag.,' vol. vi, p. 81) gives this as 

 living in the Vaal River, South Africa. 



