The Collaborative International Dictionary
topshells
Trochus \Tro"chus\, n.; pl. Trochi. [NL., fr. Gr. ? a wheel.] (Zo["o]l.) Any one of numerous species of marine univalve shells belonging to Trochus and many allied genera of the family Trochid[ae]. Some of the species are called also topshells.
Wiktionary
topshells
n. (plural of topshell English)