6. The Volutidæ, embracing the Volutes and "Boat-shells" (Cymba).
7. The Cypræidæ, or Cowries ([Fig. 12]), which owe their high polish to the size of the shell-secreting organ (mantle), whose edges meet over the back of the shell, concealing it within its folds. With these is classed the "China-shell" (Ovulum).
Fig. 11. Conus vermiculatus.
The second group, or Holostomata, is divided into nineteen families, beginning with—
1. The Naticidæ, whose type, the genus Natica, is well known to all shell-collectors through the common Natica monilifera of our coasts.
2. The Cancellariadæ, in which the shells are cancellated or cross-barred by a double series of lines running, one set with the whorls, and the other across them.
3. The Pyramidellidæ, which are high-spired, elongated, and slender shells, with the exception of the genus Stylina, which lives attached to the spines of sea-urchins or buried in living star-fishes and corals.