76 PALEONTOLOGY 



replaced by others of an opposite character (Trophon, Neptunia, 

 and TricJwtrojris), now inhabiting the Arctic and boreal coasts. 

 The entire number of fossil Muricidce amounts to 1000, or 

 about half as many as the recent. The older tertiaries of Eng- 

 land also contain species of Triton, Cassidaria, Cancellaria, and 

 Pyrula, shells (now foreign to our seas), which have formerly 

 been included in this family. As regards bulk, there are no 

 fossil species of Fusvs, Triton, and Cassis (or Stromhis and 

 Volutaj to compare with those of the present day. 



Conidcc. — The Cones and Pleurotomas appear first in the 

 chalk, and are abundant in the eocene, accompanied by an 

 intermediate form (Conorbis, fig. 19, 3), and another extinct sub- 

 genus (Borsonia, fig. 1 9, 4), in which the column is plaited, as in 

 Mitra. The genus Terebra is more common in the miocene. 



Volutidw. — The Volutes also appear as cretaceous fossils 

 in Europe and Southern India ; they are very abundant in the 

 London clay, and one occurs in the English crag. The ancient 

 species are mostly distinguished by their spires being acute, 

 as in Mitra (fig. 19, 5), a peculiarity only found in one very 

 rare living (V) species, dredged from a bed of dead shells in 

 132 fathoms water (792 feet) off the Cape. The crag Volute 

 resembles the Magellanic form. Cymba olla, the only living 

 European Volute, is a fossil in the pliocene of Majorca. 



Cyprmidw. — The Cowries form another group of subtro- 

 pical shells once common in the temperate zone. Several 

 large species are found in the London clay, most nearly related 

 to the southern Cyprovula; whilst the crag contains only 

 members of the sub-genus Trivia, one of which still lives on 

 our coast. 



The round-mouthed shells {Holostomatci), whether animal- 

 feeders or vegetarians, make a conspicuous figure amongst the 

 fossils of an earlier period than that in which the last group 

 began to flourish. The carnivorous Naticidw and Pyramid < 7- 

 lidce arc represented in the palaeozoic strata by Naticopsis, 



