CHAP. III. FAMILIES OF THE ZOOPHAGA. 63 



of ordinary dimensions, and drawn back into the shell 

 with the animal. 3. The VOLUTID.E, or volutes, having 

 the mantle much developed in the typical species : the 

 column of Ahe 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^EID^E, or cowries, whose shells are without 

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

 the bullas. 5. The STROMBID^:, 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 MURICID^E, or whelks, are resolvable again 

 into the following sub-families, each of which contains 

 genera and sub-genera : 1 . The MuricincK, or murexes * ; 

 2. The Cassince, or helmets ; 3. The Buccinince, or 

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

 Nassincs. These we shall now enter upon in the above 

 order of arrangement. 



(56.) The MURICIN.S; is a very diversified and (from 

 the little yet known 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 

 animal, 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 

 own, or by extraneous marine substances. The typical 

 genus is Murex, 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. 



