ZOOLOGY. 261 



strong, and heavy, from which circumstance they have 

 obtained the name of Rock-Shells. 



27. Trochus. Top-Shell. Inhabitant a S'/m^. ^ 



Shell spiral, conical ; aperture angular, sometimes three or 

 four sided, or with the angles rounded ; columella 

 oblique. Plate 5, fig. 27. There are three families iu 

 this genus : * erect, Columella perforated : ** Im-' 

 perforate, erect, ^slth the umbilicus closed : *** Taper- 

 ing, with an exerted Columella^ and falling on the 

 side when placed upon the base. 



Most kinds are marine, and some few are found on land 

 in moist places ; the generality of them reside in deep water, 

 others in shallows, that are left nearly dry at the reflux of 

 the tide ; the species are very numerous, and seyeral kinds 

 are common to the British shores. 



28. Turbo. Wreath-Shell. Inhabitant a Slug. 



5/ie// spiral : aperture yomiiA, entire, contracted. Plate 5, 

 fig. 28. The genus is composed of five families : * 

 Pillar Margin of the aperture dilated, imperforate : 

 "* solid, imperforate: *** soVid, perforate : **** 

 cancellate : ***** tapering. 



Some of the species in this and the preceding genera, are 

 Tery likely to be confounded, but by attenliTely observing 

 the round or angular form of their apertures, their proper 

 family may readily be deternained. IvIo?t of the kinds 



s 3 



