98 



POPULAR COXCHOLOGY. 



of Paludina, held together by crystallised carbonate of 

 lime ; the cavities of the shells, and their interstices, being 

 often filled with white calcareous spar. The Wealden 

 limestone of the Isle of Purbeck, known as Purbeck 

 marble, is in like manner composed of Paludina, but of a 

 much smaller species. Both these marbles were in great 

 repute with the architects of the Middle Ages, and there 

 are few churches or cathedrals which do not contain ex- 

 amples, either in their columns, monuments, or pavements, 

 of one or both varieties. The polished marble columns of 

 Chichester Cathedral, and those of the Temple Church in 

 London, are of Purbeck marble ; in other words, they are 

 composed of the petrified shells of snails that lived and 

 died in a river flowing through a country, inhabited by the 

 Iguanodon and other colossal reptiles, all of which have 

 long been extinct."* 



The dark patches and veins in these marbles are the 

 animal remains of the Paludina, and the most beautiful 

 slabs of Sussex marble are formed of the dark animal 

 matter, and the white calcareous spar contained in those 

 shells which were empty. 



Melania. Lam. (Melas Montf.) — Shell oblong, 

 either turreted, globose, or oval ; ex- 

 terior wrinkled, and the whorls often 

 ribbed, sometimes surmounted with spines 

 or knobs ; aperture pear-shaped, in some 

 a canal at the lower part ; the apex some- 

 times broken off in the adult : almost 

 all have a brown or black epidermis ; 

 operculum horny. Animal, outwardly ^ucSS^aa. 

 differing very little from the Paludina, according to Fer- 



* Mantell's Medals of Creation. 



