FOSSIL MOLLUSC A. 261 



the limestones are usually full of fossils, such as 

 Natica, Trigonia, Cyprina, Cypricardia, Pleuromya, 

 Mytilus, etc. 



Mr. Etheridge, F.R.S., states that the Oolitic (or 

 Jurassic) rocks of Great Britain have yielded up to 

 the present time no fewer than ninety-five genera, and 

 one thousand three hundred and sixty-eight species of 

 fossil bivalves alone. Indeed, they are by far the most 

 abundant forms of ancient life met with in these rocks, 

 although both Ammonites and Belemnites, and, in 

 some localities, even Brachiopods, are also very 

 numerously represented ; some species of Avicula, 

 Hinnites, Lima, Ostrea, Pecten, Perna, Pinna, Astarte, 

 Trigonia, Modiola, Cucculcea, Pholadomya, etc., have 

 a very long upward range. The total number of the 

 Oolitic Gasteropods (according to the same high 

 authority) is seventy-six genera, and one thousand 

 and fifteen species. The most numerously represented 

 of these genera are Alaria, Cerithium, Chemnitzia, 

 Nerincea, Pleurotomaria, Trochns, and Turbo. 



In the uppermost strata of the Oolitic formation 

 are the fresh-water beds at Purbeck, so crowded with 

 the still living Paludina as to constitute the famous 

 "Purbeck marble," formerly used in interior church 

 work. Associated with this univalve are Planorbis, 

 Melania, Limncea, Physa, Cyclus, Corbula, and other 

 well-known recent genera. Lulworth Cove is a 

 capital hunting-ground for them. 



The Wealden Clay, Sussex, has in places beds of 



