48 HANDBOOK OF SHELLS. 



7. In the next family, the Turritellidte, or " Tower-shells," the 

 type Turritella is spiral ; but in the allied form Vermctus, though 

 the spire begins in the natural manner, it goes off into a twisted 

 tube resembling somewhat an ill-made corkscrew. The mouth 

 in this family is often nearly round. 



8. The Melaniada, and 9, The Paludinidce, are fresh-water 

 shells. The former are turreted, and the latter conical or 

 globular. Both are furnished with opercula, but the mouth in 

 the first is more or less oval and frequently notched in front, 

 while in the latter it is rounded and entire. 



10. The lAtorinida t or Periwinkles, need no word from us. 



11. The Calyptraida comprise the "Bonnet-limpet," or 

 Pikopsis, and " Cup-and-saucer-limpets " (Calyptrtzd). They 

 may be described briefly as limpets with traces of a spire left. 

 The genus Phorus, however, is spiral, and resembles a Trochus. 

 They have been called " Carriers " from their strange habit of 

 building any stray fragments of shell or stone into their house, 

 thus rendering themselves almost indistinguishable from the 

 ground on which they crawl. 



12. The Turbinida, or " Top -shells," are next in order, and 

 of these the great Turbo marmoreus is a well-known example, 

 being prepared as an ornament for the whatnot or mantelpiece 

 by removing the external layer of the shell in order to display 

 the brilliant pearly nacre below. These mollusca close their 

 mouths with a horny operculum, coated on its exterior by a thick 

 layer of porcelain-like shelly matter. With them are classed 

 the familia-r 7'roehus and other closely allied genera. 



13. The Haliotidce offer in the representative genus Haliotis, 

 or the "Ear-shell," another familiar mantelpiece ornament. 



14. The Tanthinidce, or "Violet-snails," that float about in 

 mid- Atlantic upon the gulf-weed, and at certain seasons secrete 

 a curious float or raft, to which their eggs are attached, are next 

 in order, and are followed by 



15. The Fissurellidcz, or "Key-hole " and "Notched limpets," 

 whose name sufficiently describes them. To these succeed 



1 6. The NeritidcB, an unmistakable group of globular shells, 

 having next to no spire and a very glossy exterior, generally 

 ornamented with a great variety of spots and bands. 



1 7. The Patellidce, or true Limpets, are well known to every 

 sea-side visitor ; large species, as much as two inches across, are 

 to be found on the coast of Devon, but these are pigmies com- 

 pared with a South American variety which attains a foot in 

 diameter 



1 8. The Dcntal'iadcc, represented by the genus Dentalinm, or 



