246 



THE WONDERS OF GEOLOGY. Lect. III. 



few species of shells. The whole of these forms must be 

 familiar to you, as they belong to genera which swarm in 

 our present seas. The Cyprcea, or Cowry {Lign. 38, fig. 1 ), 

 and the Ancilla, or Olive {fig. 2), are well-known types. 

 The Cerithium {fig. 4), belongs to a genus most abundant 

 in the sands of the Paris basin, and is remarkable for the 

 elegance and variety of the fossil species, which exceed by 

 three times in number their living analogues. The Ceri- 

 thium giganteum attains a considerable magnitude. Some 

 masses of the Bognor rock are almost wholly composed of 

 a species of Pectunculus, {fig. 8.) The Ampullaria 

 {fig. 7) is abundant at Grignon, and commonly in a 

 beautiful state of freshness. 



It has already been observed, that the shells of fresh- 

 water mollusca possess characters by which they may be 

 distinguished from marine species. This small selection 

 {Lign. 39) from the fresh-water beds of Paris will serve to 

 illustrate this remark. The general appearance of these 

 shells will remind you of certain kinds which inhabit our 

 ponds and rivers ; particularly the large thin snail {Limnaa,* 

 fig. 5), and the discoidal shell {Planorbis, figs. 6, 7, 8) ; 

 while figs. 3 and 4, {Cyclostoma,) resemble a species that 

 inhabits the banks of lakes. At Headon Hill, Binstead, 

 Calbourne, &c. in the Isle of Wight, the clays and lime- 

 stones are full of fresh-water shells. 



33. Fossil Nautilus. — Several species of Nautilus 

 are found in the tertiary strata at Highgate, Sheppey, and 

 Bognor ; those inclosed in the septaria, or indurated argil- 

 laceous nodules, of the London clay, possess considerable 

 beauty, and admit of being cut into sections, which admirably 



* The Limncea and Planorbis are generally joint inhabitants of our 

 pools and streams. They are pulmoniferous, that is, possess air- 

 breathing organs; hence they are obliged frequently to rise to the 

 surface of the water to respire the air. — See Plate I. of my Geology of 

 the Isle of Wight : in that work the name of the first genus is erro- 

 neously printed Limneus. 



