2. Trochus. The Top Shell. Sixty-nine species.
This genus derived its name from its resemblance to a top.
The shells are marine, found in almost all parts of the world; some are smooth, but the greater number are covered, with knobs, spines, tuberculations, or undulations.
The long spines on the margin of the T. Solaris are placed at regular distances, and resemble the rays of the sun. Many, when decorticated, look like mother-of-pearl; others have a splendid metallic lustre. The T. agglutinans possesses the faculty of covering itself with extraneous substances, such as stones, corals, fragments of shells, &c. Of this species there are two kinds, which, though conchologically known only by one name, are familiarly known by two; the Conchologist and the Mineralogist; the former so called from being loaded with shells, and the latter with stones, &c. Sometimes the Conchologist is loaded with corals only, and then is called the Zoologist.
Shell thick, generally pearly, shaped like a top, spire sometimes depressed, sometimes elevated and pointed at the summit, sharp or carinated at its circumference, umbilicated or not; aperture depressed, angular or sub-angular, sometimes heart-shaped, with edges disunited; the right sharp; the columella arched, twisted, and often projecting forward; operculum horny, thin, with numerous spiral whorls, narrow, and increasing a little from the centre to the circumference.
Trochus imperialis.
T. longispina.
T. solaris.
T. Indicus.
T. radians.