part 4] THE NON-MAEINE MOLLITSCA OF CLACTON-ON-SEA. 633 



Valtata antiqua Sowerby. 



This species occurred, not uncommonly, only in Bed /, and, if we 

 judge from their condition, the specimens found are certainly 

 derivatives. This is an early Pleistocene form known only from 

 Grays, Kelvedon, Hoxne, and Swanscomb. It has hitherto never 

 occurred with VaJvata piscinalis (Mtiller), and in this case the 

 two species are assuredly not contemporary. 



Unto littoealis Lamarck. 



This form attains its maximum of size in these beds, one pair 

 in the British Museum (Natural History) measuring 69 X 47 X 28 

 mm. Crayi'ord examples come next in size, while the shells from 

 Barnwell, Swanscomb, and Peterborough are much smaller. This 

 is merely the result of environment, for the species prefers mud to 

 gravel. 



COEBICULA ETUMINALIS (Muller). 



Decidedly rare at Clacton, and apparently occurring only in the 

 Estuarine Bed. There again the condition of the specimens leads 

 one to infer that they are derivatives. 



Anodonta anatina (Linn.). 



A rare Pleistocene fossil, the only other locality for it being 

 Grays. 



Conclusions. 



Though we have always borne in mind the probability that a 

 river-deposit might contain derivatives, and thus lead to confusion, 

 this is the first instance in which we can say definitely that this is 

 exactly what has occurred. Besides the three species that we have 

 already claimed as derivatives {Yalvata antiqua, Vivipara cliluvi- 

 ana, and Corhiaila fluminalis) there are examples of Limncea 

 pereger and Bithynia tentaculata which we would place in the 

 same category; but, since there are abundant contemporary 

 examples of these two species, no confusion is likely to arise. In 

 all probability, these derived specimens have been washed out of an 

 early Pleistocene deposit of the same age as Swanscomb: that is, 

 High Terrace of the Thames. As further evidence in support of 

 inn- view, we may mention that Bed y yielded rolled examples of 

 two marine species, Purpura lapillus (Linn.) and Nuciila sp., as 

 well as three indeterminable examples which are probably of 

 Eocene age. 



These beds are clearly of one age, and no great interval of time 

 separates the highest from the lowest. In our opinion they belong 

 to the same Pleistocene stage as the Woodston, Orton Waterville, 

 Barnwell Abbey, Grantchester, llford (Uphall), West Wittering, 

 ami Stutton deposits. In several of these there can be read the 

 same physical history. 



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