PECTINIBRANCHES. 107 



within a dorsal cavity which opens by a wide fissure above 

 the head. The sexes are separate ; and, with a very few 

 exceptions, the species are covered with a turbinate shell, 

 whose aperture the snail has the power of closing, when re- 

 tracted, with a lid or operculum attached to the dorsal and 

 posterior part of the foot. They constitute by far the most 

 numerous di vision of Gasteropods, embracing probably not less 

 than eight-tenths of all univalve shells, and you can at once 

 form a general idea of the order by examining the periwinkle 

 and whelk. In the former of these you will observe that 

 the aperture is entire, that is, the lip is continuous all round 

 the mouth without break or fissure, while the latter has a 

 canal at its lower part prolonged into a sort of spout. Shells 

 formed like the first constitute Cuvier's family Trochoides, 

 including, among others, the genus Trochus, now partitioned 

 into many subgenera characterised by having a conical spiral 

 shell with a quadrangular mouth pearly in the throat ; the 

 Turbo, in which the shell is turbinate and the aperture 

 round ; the Paludina, which has a similar but unsilvered 

 aperture, and is a native of fresh waters ; the Littorinae, like 

 this in character, but an amphibious race, frequenting the 

 sea-shores, and indifferent whether it is submerged or left 

 dry by the recess of the tide ; the Nerita, known 'by its 

 semilunar mouth and its depressed spire ; the Phasianella, 

 one of the prettiest genera, speckled like the pheasant or 

 guinea-hen ; and the lanthina, which is non-operculate, but 

 provided instead with a cellular float to support it at the 

 surface of the sea. The second family of the order is named 

 Capuloides, in which the shell is oftenest simply conical like 

 a limpet, but sometimes there is a small lateral spire, the 

 interior exposed, however, by the disproportionably large 

 aperture, which is entire and never protected with an oper- 

 culum. The genera are few and sparing in species ; nor is 

 there any common example, excepting I can quote as such 

 the shell called the Hungarian-bonnet by collectors, the 

 Capulus of science. The third family, or Buccinoides, may 

 be represented by the whelk, but it includes, in its wide 

 embrace, many shells which have no canal but where the lip 

 of the mouth is merely interrupted by a sinus or emargina- 

 tion. Hence we find in it the beautiful Cones (Conus) and 

 Cowries (Cypraea) the glory of every rich collection, and 

 whose deficiency declares the poverty of mine the Ovulae 

 and the Volutes (Voluta), inferior to none in attraction and 

 sportive variety. The whelk (Buccinum) gives its name to 

 the family as being its typical genus ; and it is followed by 

 the turreted Cerithium, the spinous rock-shells (Murex), 



