BITHYNIA TENTACULATA. 35 



Specific Characters. — Shell small, naticoid ; whorls few, smooth, the last 

 ventricose ; spire exceedingly short ; mouth entire, large in proportion to the size 

 of the shell, oval, angiilate above; outer lip thin; inner lip callous; umbilical 

 slit rimate. 



Dimensions. — L. 5 ram. B. 5 mm. 



Distribution. — Reamt : River Danube. 



Fossil : Icenian Crag — Wet/hourne zone : East Run ton, North 

 Walsham boring. 



Pleistocene deposits near Berlin. 



Remarks. — For the discovery of this interesting shell in the AYeybourne Crag 

 we are indebted to Mr. C. Reid. At present it is only known in a living state 

 from the Danube. Its occurrence in the newest zone of the English Crag, the 

 marine fauna of which is of a boreal character, seems at first sight anomalous, but 

 we may remember it was associated at a later period with Corhicula fluminalis, 

 a species now generally characteristic of warmer climates than our own, but 

 exceedingly abundant in England during the Pleistocene epoch. The winters in 

 the Danubian region, however, are at present often severe; these molluscs were 

 probably able to adapt themselves, as now, to different conditions. Their 

 disappearance from western Europe may have been due to the competition of 

 allied and stronger forms. 



Clessin identifies L.fuscns with L. naticoides, an apparently different though 

 allied species living in the Danube and found locally but plentifully in France 

 (Ardennes) ; it is reported also from Belgium, Grermany, Moravia and Galicia 

 (J. W. Taylor). 



L. fnscus appears to be fairly abundant in the Weybournian Crag at East 

 Runton ; it was met with also in the well-boring at North Walsham in deposits of 

 similar age, together with Telliua halildca and other marine shells. 



Genus BITHYNIA,^ Gray, 1821. 

 Bithynia tentaculata (Linne). 



1767. Helix tentaculata, Lium', Svst. Nat., ed. xii, p. 1249, no. 707. 

 1848. Pahulina tentaculata, S. V. Wood, Mon. Crag Moll., pt. i, p. Ill, tab. xii, fig. 2. 

 1853. Bithinia tentaculata, Forbes and Hanley, Brit. Moll., vol. iii, p. 14, pi. Ixxi, figs. 5, 6. 

 1862. Bythinia tentaculata, Jeffreys, Brit. Conch., vol. i, p. 60, pi. iv, fig. 4. 

 1890. Bythinia tentaculata, C. Eeid, Plioc. Dep. Brit., p. 228. 



1897-1901. Bythinia tentaculata, Kennard and B. B. Woodward, Essex Nat., vol. x, pp. 93 et seq., 

 1897; Proc. Malac. Soc, vol. iii, p. 199, 1899; Proc. Geol. Assoc, vol. xvii, pp. 217 etseq., 1901. 



1 According to the Rev. G- Frank Knight and Mr. B. B. Woodward, this generic name, first sug- 

 gested by Leach, was derived from Bithynia in Asia Minor, and not from ^vdim, as stated by Jeffreys. 



