CHAP. III. FAMILIES OF THE ZOOPHAGA. 63 



of ordinary dimensions, and drawn back into the shell 

 with the animal. 3. The Volutid.^, or volutes, having 

 the mantle much developed in the typical species : the 

 column of the shell is always marked by regular and 

 well-defined plaits, nearly the same as in the last; but 

 the base of the aperture is obtuse, truncate, and notched. 

 4. The Cypr^id^, or cowries, whose shells are without 

 any spire ; the last whorl enveloping all the others, as in 

 the bullas. 5. The Strombid^e, or wing-shells ; the 

 only division where the outer side or lip of the aperture 

 is considerably dilated. The two first of these are the 

 typical and sub-typical groups ; the three latter form- 

 ing the aberrant circle. The whole are marine. 



{55.) The MuRiciDiE, or whelks, are resolvable again 

 into the following sub-families, each of which contains 

 genera and sub-genera : ] . The Muricince, or murexes * ; 

 2. The Cassinw, or helmets ; 3. The Buccinincp, or 

 whelks ; 4. The PurpurincE, or purpuras ; and, 5. The 

 NassincB. These we shall now enter upon in the above 

 order of arrangement. 



(56.) The MuRiciN^ is a very diversified and (from* 

 the little yet knowni of the animals) a very difficult 

 group to arrange. Generally speaking, they are strong 

 shells, of a rough exterior, without any plaits or teeth 

 either upon the pillar or outer lip : the different periods 

 of their growth, or rather of their enlargement by the 

 anim.al, are marked by thickened transverse ribs called 

 varices, which are differently disposed in the genera : the 

 canal is generally short, or of moderate length, but always 

 present, and usually a little bent on one side. The aper- 

 ture is oval; and the spire nearly as long as the body- whorl. 

 They chiefly abound in the shallow waters of temperate 

 seas; and are either covered with an epidermis of their 

 owai, or by extraneous marine substances. The typical 

 genus is MureJc, where we find some of the most beau- 

 tifully coloured shells, and certainly the most elaborate 

 in structure, among the whole of the spiral univalves. 



* Sometimes called rock-shells, from the roughness and irregularity of 

 their surface. 



