Cassis madagascariensis spinella Clench, 1944 Cassis madagascariensis, common name the queen helmet, is a marine gastropod mollusc in the family Cassidae, the helmet shells and bonnet shells.It is known for being the largest species of its family in the Atlantic Ocean.

[1] This species occurs in the tropical Western Atlantic, the Gulf of Mexico and the Caribbean Sea.

The specific name "madagascarensis" literally means "of Madagascar", but this was a misunderstanding of the type locality by the original author.

[2] This shell typically has three rows of blunt knobs and smaller lines of spiral folds.

Emperor/Queen Helmet Snails frequently observed (photographed) in depths as shallow as two feet.