GASTEROPODOTJS MOLLTJSCA. 247 



of" luccinum. A few only of the tertiary gene'ra are now 

 entirely unknown in a recent state ; as, pileolus, omalaxon, 

 and pleurotomaria ; and some entire genera of this class, at 

 present inhabiting the waters of the globe, have not yet 

 been met with in any of the tertiary strata, as rotella, 

 magilus, stomatia, navicella, scarabceus, succinea, anostoma, 

 vitrina, testacella, and dolabella. 



Many genera of gasteropods, most abundant in existing 

 species, present comparatively few fossil species in the ter- 

 tiary formations : thus, three hundred and twenty-five living 

 species of helix are at present known, and only thirty-five 

 species of that terrestrial pulmonated genus have been 

 observed in the tertiary strata. Although one hundred and 

 four living species of patella are known to inhabit the ocean, 

 only ten fossil species have been recognised in the tertiary 

 marine formations ; of neritina, there are sixty known recent 

 species, and only seventeen tertiary fossil species ; ofhaliotis, 

 twenty-nine recent, and one tertiary fossil; trochus, one 

 hundred and three recent, and seventy tertiary fossil ; mono- 

 donta, forty-two recent, and eight fossil ; strombus, forty- 

 five recent, and nine fossil ; buccinum, one hundred and forty- 

 three recent, and ninety-five tertiary; mitra, one hundred 

 and twelve recent, and sixty- six tertiary ; cypraa, one hun- 

 dred and thirty-five recent, and nineteen tertiary; conus, one 

 hundred and eighty-one recent, and forty-nine tertiary fossil 

 species, and only one of all these species of coni is found to 

 be common to the tertiary and the recent epochs. In most 

 of the genera of gasteropods, however, as in other classes of 

 animals, there are several species which have survived the 

 tertiary deposits, and still continue to exist in a living state. 

 Seven species of cyprcea are found common to the ter- 

 tiary formations and our present seas; twenty species of 

 luccinum are both tertiary and recent ; six species of cassis, 

 six of triton, fifteen of murex, eleven of fusus, seven of ceri- 

 thium, twelve of trochus, nine of natica, and the same number 

 of tertiary species of helix, are found still living on the con- 

 tinent of Europe. 



The PTEROPODA swim by musculo-membranous expansions 

 of the mantle, which project from the sides of the head. 

 Their body is naked, or is partly protected by a delicate 

 shell. They are small animals that float on the surface of 



