Plagiostomi — Sharks and Rays. 



The families of Carchariidm and Lamnidce appear to be the Wall-case, 

 characteristic Sharks of modern times. Detached teeth, vertebras, No - 3 - 

 and portions of calcified cartilage are abundantly met with in l ^o!' 

 Cretaceous and Tertiary formations, but scarcely any are discovered 

 so low in the geological series as the Jurassic. The Cretaceous 

 Corax is possibly allied to the living Carcharias ; and other Car- 

 chariidce found fossil in the Tertiaries are Galeocerdo, Zi/gana, 

 ("Hammerheads"), etc. The Lamnidce are represented by Car- 

 charodon, Otodits, Lamna (Fig. 14), Oxyrhina, and others; and the 

 remains of the first-named genus are especially worthy of note. 

 The teeth of Carcharodon (Fig. 15) seem to occur first in the 



Fig. 14. 



Fm. 15. 



Fig. 14. — Tooth of Lamna elegatis, 

 Agassiz, London Clay. 



Fig. 15.— Tooth of Carcharodon megalodon, 

 Agassiz, Suffolk Crag. (One-third nat. size.) 



Upper Cretaceous of Maastricht, Holland, and those of Tertiary 

 times have an almost world-wide distribution. Teeth of the largest 

 species are exhibited from New Zealand, Australia, South Carolina, 

 the West Indies, France, Spain, Italy, Malta, and Arabia, and 

 from the Antwerp and Suffolk Crags. 



It is also interesting to notice that in some places, both in the 

 Atlantic and Pacific (especially at extreme depths in the red-clay 

 areas), the "Challenger" dredged up many teeth of Sharks and 

 tar-bones of "Whales, all in a semi-fossil state, and usually impreg- 



Fig. 16.— Teeth of Notidanus gigas, Red Crag, Suffolk. 



nated with oxides of iron and manganese. The Sharks' teeth belong 

 principally to species believed to be extinct, and resemble those 

 found fossil in the late Tertiary formations. 



The small Scyllitdcd appear to be represented in the English Table-case, 

 Chalk by Scylliodus ; and the living genus Scyllium, with some No - 27 - 



