240 MOLLUSCA FfiOM THE AECTIC BED. [JuilG I912, 



deposits is not well marked, ^-^e were able to obtain a number 

 of moUusca from these u^^per beds, namely : — 



Vitrea radiatula (Alder). ^ Planorhis alhus Miill. 



Hygromia Mspida (Linn.). JPlanorhis umhilicatus Miill. 



Hygromia liherta} West. Flanorbis carinatus Miill. 



Relicigona arhustorum (Linn.). ' Vcdvata jpiscinalh (Wviii^. 



Succinea elegans Risso. Bithyvia tentoculafa (Linn.). 



Limncsa cmricularia (Linn.). Bithynia leachii (Shepp.). 



Flanorhis contcn^his (Linn.). Neriiina Jhiviatilis (Linn.). 



Planoj'his crista (Linn.). TJnio tumidusHetz. 



Planorhis leucostoma Millet. Fisidium amnicum (Miill.). 



These are all normal shells, and exhibit none of the dwarfing 

 so noteworthy in the Pleistocene examples. The contrast between 

 the two faunas is very marked, although a nnmber of species are 

 common to both. 



In conclusion, we have to thank Mr. E. A. Smith, I.S.O., for 

 his very kind assistance in the determination of some of the 

 examples. 



Supplementary Note on a Collection of Mollusca from 

 the Arctic Bed in the Angel Eoad Ballast-Pit. 



Mr. "Warren also sent ns another series of molluscan remains 

 obtained at Angel Koad, and twenty species were represented. 

 These are enumerated in the last column of the table (p. 234). 



It will at once be noticed that this fauna is practically the same 

 as that from Ponder's End : for, excluding the Pisidia, there is only 

 one species, Succinea elegans Piss., that did not occur at the latter 

 locality. This species has a decidedly northern range. Its limit 

 in Sweden is the isotherm 10° to 12° C, and in Finland 8° to 10° C, 

 thus confirming the views which we have already expressed. 



All the Fisiclia are dwarfed, and the conditions were evidently 

 not favourable. There is the same dwarfing of certain species 

 and the abundance of others as at Ponder's End, and there can 

 be no doubt that they are of the same age and represent similar 

 conditions. 



EXPLANATION OF PLATE XVII. 



[The dimensions are shown in millimetres.] 



Fig. 1. Succinea (cf. S. grmnlandica Beck). (See p. 238.) 



2. Succinea schumacheri Andrese. (See p. 238.) 



3. LimncBa palustris (Miill.) var. (See p. 236.) 



4. Limncea truncatula (Miill.) var. (See p. 236.) 



5. Sphyradium columella Gr. v. Mts. (See p. 235.) 



6. Vertigo 'parcedentata A. l^YSMw. (See p. 235.) 



7. Valvata piscinalis (Miill.). (See p. 238.) 



8. JPlonorbis arcticus Beck. (See p. 237.) 



9. Bisiditim stiphiunt A. Schmidt. Eight valre of young specimen. 



10. P. nitidum Jenyns. Eight valve : dwarfed form. (See p. 239.) 



11. P. pusiUinn (Gmel.) Jenyns. Left valve of young specimen. 



^ —H. sericca, Drap. of Continental authors, no7i Miiller 



