149 



Mediterranean ; the latter also extends far north to Greenland 

 and Novaya Zemlia and according to Gwyn Jeffreys, is ex- 

 tensively distributed throughout the North Atlantic to the 

 North Eastern Coast of America. 



Besides these two local species there is another. A. 

 triangularis, found locally on all the British Coasts and ex- 

 tending to the Canaries ; whilst about twenty other species 

 flourish in the Northern and Arctic Seas of Greenland, Iceland, 

 Norway. Northern Europe, and North America. Tims it 

 will be seen that the genus at the present day is of essentially 

 northern distribution, and associated with cold climates. 



Turning now to the palaeontology of the genus, we find 

 that the three British species are found fossil in the Pliocene 

 deposits of Norfolk and Suffolk, where, however, they 

 occur with nearly twenty other species most of which 

 are extinct. Further back in time the living forms 

 do not 20. and omitting the Miocene Astartes which do 

 not occur in Britain, we meet with the group again in the 

 lower Eocene beds of the South of England, whence half- 

 a-dozen species have been recorded.* It is also numerous in 

 the Tertiary deposits of the Continent and North America. 

 In these formations, however, it is associated with animals 

 and plants having a decidedly troiiical aspect, indicative of 

 warm climates. 



Several species occur in the Cretaceous formations, but 

 not until the Jurassic is reached does the genus attain its 

 maximum dimensions. In this great geological system, the 

 species are perhaps most numerous in the Upper Corallian 

 and Lower Kimmeridgian strata, where they are so abundant 

 that they constitute a definite geological horizon, known to 

 continental geologists as the Astartian. Even in the Upper 

 Oolitic strata of North Eastern Yorkshire they are com- 

 paratively abundant, over a dozen species having been 

 obtained, and of which the commonest is Astarte duboisiana 

 from the Coralline limestone of Pickering and neighbourhood. 

 Altogether nearly 300 species of fossil Astarte are known 

 and attain their maximum development in the Secondary 



* Bullen Newton, Catalogue of British Eocene and Oligocene 

 Mollusea. 



