638 MOLLUSC A CLASS IV. GASTROPODA. 



spirally, and with spiral stride. The members of this family, also, chiefly 

 inhabit southern seas. 



The MITKID^E are more cylindrical shells than the preceding, with more 

 or less acute spire and narrow aperture, without operculum ; the columella 

 bears several folds, of which the hindermost, i.e., the one furthest from the 

 well-marked anterior canal, is the largest. The Mitridse are tropical shells, 

 the best-known examples being, perhaps, Mitra episcopcdis, which is white, 

 with squarish, red spots arranged in rows. 



The VOLUTID^J include some of the finest of the tropical shejls. The 

 animal has a long foot and a wide, flat head ; the shell varies, being spindle- 

 shaped in some, and greatly swollen in others ; in all, however, the aperture 

 is large, the outer lip slightly turned out, the margin simple, notched for the 

 siphon at the anterior end next the columella, which ends in a point, and 

 bears several folds. The protoconch is set obliquely. 



The MARGINELLID^E have oval, or sub-conoidal, shells that are shining and 

 polished, without operculum. 



The HARPID.E include but a single genus, Harpa, to the shell of which the 

 periodic mouths impart its characteristic lirate appearance. The spire is 

 short, the aperture wide, lip simple, with anterior siphonal notch ; there are 

 no folds on the columella, nor is there any operculum. The Harps are found 

 in tropical seas, and so, too, are olives, which come next. 



The OLIVID;E, or olives and rice - shells, in point of polished surface 

 and in colour-markings, are equal to the cowries. They are more or less 

 cylindrical, with a short spire and long, narrow mouth; the columella is 

 callous, and bears several plaits towards the anterior extremity an oper- 

 culum is sometimes present. 



Sub-order 5. TOXOGLOSSA. The radula normally has the formula 1/0 1, 

 and the teeth are large. 



The CANCELLARIID^E include but one genus, Cancellaria, so named from 

 the cancellate, or cross-marked sculpturing of the shell, which is oval, or 

 turreted, with anterior siphonal notch ; the columella is strongly plicate ; the 

 operculum is wanting. 



The PLEUROTOMIDJE include a great number of spindle-shaped shells, most 

 of which bear a characteristic notch in the outer lip, and a marked anterior 

 canal ; the columella is smooth ; the operculum is not always developed. 



The CONID.E are too universally known to require description, their 

 conical shells, with long, narrow apertures, are only approached in form in 

 one or two exceptional instances by members of other families. The 

 operculum, when present, is very small, and almost rudimentary. Perhaps 

 the most remarkable feature about the animal lies in its radula, the teeth 

 of which are proportionately large, are barbed, and perforated by a duct 

 leading to a poison gland. This character has not been observed in any 

 other group. The cones are essentially tropical inhabitants. The varied 

 markings of their shells are completely concealed during the lifetime of the 

 occupant by the tough periostracum in which they are enveloped. 



The TEREBRID^?, or auger shells, are extremely long and slender, with 

 many whorls, which are sometimes smooth but often ribbed ; the mouth is 

 oblique, with simple, thin lips and large anterior notch ; the columella is 

 without folds. The horny operculum is bluntly claw-shaped. The sole 

 genus, Terelra, is entirely confined to tropical seas. 



