An order of gastropod Mollusca having a heart with two auricles and one ventricle. The shell may be either spiral or shieldlike. [
1913 Webster]
" It is now usually regarded as including only the Rhipidoglossa and the Docoglossa. When originally established, it included a heterogenous group of mollusks having shieldlike shells, such as Haliotis, Fissurella, Carinaria, etc."
[1913 Webster]