58 



THE GEOLOGICAL DISTRIBUTION OF EXTINCT 

 BRITISH NON-MARINE MOLLUSCA. 



By R. BULLEN NEWTON, F.G.S. 



(Read before the Society, Sept. 12th, iqoo). 



The following work has been compiled in order to show at a glance 

 the geological range of every recorded species of terrestrial and fluvia- 

 tile shell, excluding those with M.S. names and any forms insufficiently 

 described, from the strata of the British Islands, which are regarded 

 as non-existent within the same limits. 



Among such molluscs, Archanodon Jukesi appears to be the most 

 ancient. It is related to the modern Anodonta, and belongs to the 

 Devonian or Old Red Sandstone period, having been found in Ireland, 

 Monmouthshire, and Northumberland. Next in point of age are a 

 number of species peculiar to the Coal Measures, exhibiting unioni- 

 form affinities, which have been recognised by Wheelton Hind and 

 others under the genera Anthracomya, Carbontcola, and Naiadites. 



Land shells make their first appearance in rocks of Lower Lias age, 

 forms having been described by Charles Moore as referable to the 

 genera Valvata, Vertigo, Despcena, Platiorbis, and Helix, which were 

 discovered in the Charteris House Lead Mine, Mendip Hills, 270 feet 

 from the surface. 



More than sixty years ago William Bean described and figured Uiiio 

 distorhis from the Inferior Oolite beds of this country. This unique 

 specimen, now in the possession of the British Museum, was found at 

 Gristhorpe, Yorkshire. 



Through the researches of Edward Forbes, Ralph Tate, and others, 

 w^e have been made acquainted with an interesting assemblage of shells 

 occurring in the Oolite (Infra-Oxfordian) rocks of Skye and Raasay in 

 Scotland, containing such genera as Leptoxis, Neritiiia, Paludestrina, 

 Valvata, Viviporus, Corbicula, and Unio. The Purbeck and Wealden 

 strata have yielded a fauna of freshwater or estuarine character, among 

 the mollusca being Afelania, Melanopsis, Physa, Unio, etc. 



In Tertiary times a large number of terrestrial and fluviatile shells 

 flourished, nearly all of which belong to extinct species. One of the old- 

 est forms from this group of rocks is Cainptoceras priscum, a member of 

 the family Physidse, which was described by H. H. Godwin-Austen, in 

 1882, from the London Clay Deposits of Sheppey. During the suc- 

 ceeding Post-Tertiary period these mollusca were very abundant and 

 mainly belonging to species which survived to modern times, only 

 about twelve Gastropods being recognised as extinct besides three or 

 four Lamellibranchs. 



