GASTEROPODA. 91 



number of fossil Muricidce amounts to 1000. or about half as 

 many as the recent. The older tertiaries of England also 

 contain species of Triton, Cassidaria, Gancellaria, and Pyrula, 

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

 included in this family. 



Conidce. — The Cones and Pleurotomas appear first in the 

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

 intermediate form (Conorbis, fig. 28, 3), and another extinct 

 sub-genus (Borsonia, fig. 28, 4), in which the column is 

 plaited, as in Mitra. The genus Terebra is more common in 

 the miocene. 



Volutidce. — 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 (fig. 28, 5) are mostly distinguished by their 

 spires being acute, as in Mitra, a peculiarity only found in one 

 very rare living (?) 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, 



' Cyvrwidce. — The Cowries form another group of sub- 

 tropical 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. 



As regards bulk, there are no fossil species of Fusus, 

 Triton, Cassis, Strombus or Voluta, to compare with those of 

 the present day. The " fountain-shell " (Strombus gigas), of 

 which so many are imported from the West Indies for the 

 manufacture of cameos, may weigh 5 lbs. 



Holostomata* — The round-mouthed shells, whether animal- 

 feeders or vegetarians, make a conspicuous figure amongst the 



* Gr. holos whole, and stoma mouth. 



