KENNAED & WOODWARD : ON HOLOCENE MOLLTTSCA. 95 



in Suffolk. On the Continent it is known from Ribe, in Denmark, has 

 been recorded from rejectamenta of the sea on the Belgian coast near 

 the French frontier,' and has been taken on the German coast ^ on the 

 banks of the dykes of the Dollart in the estuary of the Ems, and 

 at Dangast on the Jade Busen. It will be noted that it only occurs in 

 the area of the old Thames-Rhine river system, and its present dis- 

 continuous distribution is to be explained by the inroads of the North 

 Sea, submerging the old estuary. 



V. Dagenham, Essex. 



In August, 1905, Dr. Frank Corner sent us a large quantity of 

 material which had been obtained at a depth of 20 feet at Dagenham. 

 The soil is a peaty silt containing many twigs and yielding a fair 

 number of molluscan shells, as well as a few caddis-worm cases and 

 insect remains. It is obviously a river deposit, whilst the depth 

 at which it occurs shows that we are dealing with the older 

 Holocene beds, deposits which are but rarely exposed in the Thames 

 Valley, and in fact molluscan remains have only been noted from 

 four localities — Crossness, Charlton, Tilbury, and the London Docks. 

 We are able to record thirty-two species, viz. — 



Zonitoides nitidns (MiilL), 5 examples. P. leucostoma, Millet, 5 examples. 



Fyramidula rotundata (MiilL), common. P. vortex (Linn.), 6 examples. 



Helix nemoralis, Linn., 1 example. P. crista (Linn.), 2 examples. 



Helicigona arbustorum (Linn.), 2 P. fontanus [lAgVii.), 3 examples. 



examples. Bithynia tentaculata (Linn.), common. 



Ancylus JluviatiUs, Miill., 2 examples. B. Leachii (Shepp.), common. 



Acroloxus lacustris (MiilL), common. Valvata pisdnalis (MiilL), common. 



Succinea eleyans, Risso, common. V. cristata, MiilL, 8 examples. 



Ziinncea pereyer (MiilL), common. Neritina JluviatiUs (Linn.), 2 examples. 



L. palustris (MiilL), common. Unio tumidus, Eetz., 8 valves. 



L. stagnalis (Linn.), 1 example. Sphmrium corneum (Linn.), 4 valves. 



L. truncatula (MiilL), 4 examples. Pisidium amnicum (Linn.), 12 valves. 



Planorbis eorneus (Linn.), common. P. Henslowianum (Shepp.), common. 



P. umbilicatus, MiilL, common. P. Casertanum(2o\i) [ = ciHer«;««, Alder], 

 P. carinatus, Miill., 6 examples. common. 



P. contortm (Linn.), 10 examples. P. Gassiesianum, Dupuy, 2 valves. 



P. albus, Miill., 12 examples. P. pusillum (GmeL), common. 



All the examples of Pisidium Casertanum belong to the thick hinged 

 mutation. 



This collection forms an important addition to our knowledge of the 

 mollusca of the early Holocene, for there are several species which 

 were not noticed at either Crossness or Tilbury. These are Planorbis 

 Cornells, P. albus, P. carinatus, P. vortex, and Pisidium amnicum. 

 Of particular interest are the examples of Bithxjnia Leachii, which 

 resemble the recent Thames form and differ markedly from the 

 var. inflata, which was the prevalent type during the deposition of the 

 Pleistocene brick-earths of Crayford and Ilford, 



It is noteworthy that Plamrbis Strmnii is absent as at Crossness 

 and Tilbury. In the main stream it has not yet been found lower 



• Malzine (F. de), Mem. Soc. Sci. Hainault, i (1867), p. 317. 



2 Borcherding (F.), Abhandl. Naturw. Ver. Bremen, 1883, p. 330. 



