ZOOLOGY. 



261 



strong, and heaTy, from which circumstance they have 

 obtained the name of Rock-Shells. 



27. Trochus. Top-Shell. Inhabitant a Slug. 



Shell spiral, conical ; apet^ture angular, sometiraes three or 

 four sided, or with the angles rounded ; columella 

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

 this genus: erect, Columella perforated: Im- 

 perforate^ erect, with 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 refiux of 

 the tide ; the species are very numerous, apd several kinds 

 are common to the British shores, 



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



^SAe// spiral : aperture xownd^ entire, contracted. Plate 5, 

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

 Pillar Margin of the aperture dilated, imperforate : 



solid, imperforate: BoWd^ perforate : 



cancellate : tapering. 



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

 Tcry likely to be confounded, but by attentively observing 

 the round or angular form of their apertures, their proper 

 family may readily be determined. Most of the kinds 



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