MARINE ANIMALS. 89 



there are four species of Pleurotoma (including P. belgica, Goldf., 

 and P. Parkinsoni,~Des}i.) and three of Natica (N. Nysti, D'Orb., 

 N. crassatina, Lam., and N. hantoniensis , Sow.). With these 

 are associated species of Patella, Melania (M. semidecussata, 

 Lam.), Trochus, and Murex. 



Oysters are among the most abundant bivalves ; three species 

 (Ostrea callifera, Lam., O. cyathula, Lam., and O. longirostris, 

 Lam.) occur in enormous masses. Near Stetten (in the environs 

 of Basle) the great Ostrea callifera was established in large banks 

 on the Jurassic oolite, which then constituted the bottom of the 

 Tongrian sea. A similar oyster-bed is to be seen near Develier, 

 and others on one of the sides of the Mettenberg and in the 

 Delsberg, while another bed has been formed by the Ostrea 

 cyathula near Neucul. 



Of the numerous other bivalves we may mention the Lucina 

 (L. Heberti, Desh., L. squamosa, Lam., L. undulata, Lam., and 

 L. tenuistriata, Heb.), Pectunculi (P. obovatus and angusticos- 

 tatus, Lam.), Cardia (Cardium Raulini, Desh., and C. tenuisul- 

 catum, Nyst), Cyrena (C. semistriata, Desh.), Cytherea (C. Icevi- 

 gata } Lam., C. incrassata, Sow., and C. splendida, Mer.) ; abun- 

 dant forms of Tellina, Pholadomya, and Lithodomi are also 

 discovered. 



The long, cylindrical, indistinctly jointed filaments which are 

 met with on the slabs from the Three Torrents (fig. 325, p. 103) 

 may perhaps be referred to worms. 



Of the remains of large fishes, the teeth of sharks and the 

 bones of a cetacean are of most frequent occurrence. The 

 teeth of a shark (Cacharodon megalodon, Ag.), with toothed 

 margins, attain a length of 6 inches, and from them the length 

 of the whole animal has been estimated at 85 feet ; it was there- 

 fore more than twice as large as the shark of the present seas. 

 This giant was then distributed in all seas, and it also occurs in 

 the Swiss shell-sandstone. A smaller species (Lamna cuspidata, 

 Ag.) is also found in Switzerland, the narrow two-edged teeth 

 of which are provided with two long processes at the base. 



The cetacean (Halitherium Schinzii, Kaup) belongs to the 

 group of the Sirenia, those singular herbivorous animals which 

 seem to constitute the transition from the whales to the Pachy- 

 derms. One species is most nearly related to the manatees 



