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LIMESTONE FROM THE NORTH SEA. 



9 



contact with the limestone, but of very much softer character, which 

 from a preliminary examination appear to be of a coniferous nature, 

 although requiring further study before a more accurate deter- 

 mination can be attempted. 



Out of the 23 determined molluscs of this limestone 18 (or 

 nearly 80 per cent.) trace their origin from the Vindobonian 

 stage of the Miocene Period, 10 (or about 40 per cent.) may be 

 regarded as extinct, whereas 12 (or 50 per cent.) are found living 

 in recent seas. 



The extinct species include 



Streptochetus sexcostatus. 

 Fic.us \_Pyrula] simplex. 

 Ringiculella ventricosa. 

 Arcoperna sericea. 

 Nucula laevigata. 



Yolclia oblongoides. 

 Lsevicardium fragile. 

 Sinodia tertiaria, sp. nov. 

 Tellina benedeni. 

 Panopsea menardi. 



The existing species are found chiefly in British and Mediter- 

 ranean seas, although Spisula ovalis and Cyprina islandica belong 

 to more boreal waters, and are never found so far south as the 

 Mediterranean. This list embraces : — 



Ranella gigantea. 

 Turritella communis. 

 Aporrhais pespelicani. 

 Naticina alderi. 

 Actseon tomatilis. 

 Scaphander lignarius. 



Nucula nucleus. 

 Dentilucina borealis. 

 Thyasira flexuosa. 

 Cyprina islandica. 

 Isocardia humana ( = cor J. 

 Spis^t,la ovalis. 



The majority of the species recognized are fairly evenly repre- 

 sented in both the Coralline and the Red Crag deposits, 15 occurring 

 in the former and about 12 in the latter. Among them the 

 genus Yolclia, belonging at the present day entirely to Arctic seas, 

 is well distributed through the limestone, specimens having been 

 identified as Wood's oolong oides, which is known from the Red 

 Crag, Norwich Crag, and later deposits of East Anglia, although 

 never yet recorded from the Coralline Crag. Another species, 

 however, of this genus, but not occurring in the present limestone, 

 is Y. semistriata, which is restricted to Coralline Crag beds, and 

 therefore forms an illustration of the Arctic genus Yolclia having 

 been associated with a more southern fauna than prevailed during 

 Red Crag or later geological times as represented in England. 



Further support is given to the southern aspect of the fauna by 

 the occurrence in the limestone of a new Dosiniform shell, Sinodia 

 tertiaria, which presents affinities that are only to be fotmd in the 

 Indian Ocean and regions of Southern Asia. The comparatively 

 large number of extinct species is greatly in favour of the North- 

 Sea rock being of older horizon than the Red Crag, as among them 

 are Arcoperna sericea, Tellina benedeni and Panop&a menardi 

 (— gentilis), which are not known of later age in this country than 

 the Coralline Crag, although Tellina benedeni occurs as well in the 

 Lenham Beds and Panopcea menardi in the Boxstones. In con- 

 nexion with the antiquity of this fauna, mention should also be made 

 of the occurrence of Streptoclietus sexcostatus and Ficus simplex, 



