On the Australian pectens confounded with the New Zealand p. laticostatus. (gray)

The only species of the section Vola, inhabiting New Zealand-waters, is generally known under Gray's name of P. laticostatus, to which is referred P. Novae Zelandiae, Reeve, as a synonym; but neither names should be employed, inasmuch as the first is pre-occupied by a Lamarckian species fossil in Pliocene Strata in Italy, and the second by another New Zeahtnd species, established by Gray.
Eastern Australia, Tasmania, and South Australia have each a species of Vola, which has been confounded with that belonging to New Zealand.
The specific differences between these species may now be detailed as follows: - P. LATICOSTATUS is distinguished by its broad, flat, smooth ribs with perpendicular sides, two and one-third times broader than the flat furrows.
P. MERIDIONALIS has the ribs convexly depressed, concentrically lamellose, and with 1, 3, or more radial sulcations; the furrows are concave, and as wide or a little wider than the ribs.