Linda,

Vittina and quite a few other generic names for the Neritidae have not been
generally accepted because there have been so few available reference
materials on this family.  Bruce Neville and I have been working for the
last four years on a book on worldwide Neritidae and have identified quite a
few valid genera not in common use.  Most people are still using the 150
year old classification of Nerita, Neritina, and Septaria (or Navicella).
Some throw in (and wildly misuse) Clithon, Clypeolum, and Theodoxus.

Tom Eichhorst in New Mexico

As it stands at present, subject to change:

The Family Neritidae is divided into two subfamilies with the following
genera and subgenera:

Family: Neritidae Rafinesque, 1815

Subfamily: Neritinae Rafinesque, 1815

Genus: Nerita Linnaeus, 1758 (71+ species)
        Subgenus: Adenerita Dekker, 2000 (1 species)
        Subgenus: Amphinerita von Martens, 1887 (5 species)
        Subgenus: Cymostyla von Martens, 1887 (25 species)
        Subgenus: Heminerita von Martens, 1887 (1 species)
        Subgenus: Ilynerita von Martens, 1887 (1 species)
        Subgenus: Linnerita Vermeij, 1984 (8 species)
        Subgenus: Lisanerita Krijnen, 2002 (2 species)
        Subgenus: Melanerita von Martens, 1889 (13 species)
        Subgenus: Nerita Linnaeus, 1758 (1 species)
        Subgenus: Ritena Gray, 1858 (7 species)
        Subgenus: Theliostyla Mörch, 1852 (18 species)

Genus: Mienerita Dekker, 2000 (1 species)

Subfamily: Theodoxinae Montfort, 1810

Genus: Clithon Montfort, 1810 (42+ species)
Genus: Clypeolum Récluz, 1842 (2 species)
Genus: Fluvinerita Pilsbry, 1932 (1 species)
Genus: Nereina Cristofori & Jan, 1832 (2 species)
Genus: Neripteron Lesson, 1831 (15+ species)
        Subgenus: Dostia Gray, 1842
               Subgenus: Neripteron Lesson, 1831
Genus: Neritina Lamarck, 1816 (10+ species)
Genus: Neritodryas von Martens, 1869 (6 species)
Genus: Neritona von Martens, 1869 (4 species)
Genus: Puperita Gray, 1857 (1 species)
Genus: Septaria Férussac, 1807 (13 species)
Genus: Smaragdia Issel, 1869 (8 species)
Genus: Theodoxus Montfort, 1810 (approx. 30 species)
        Subgenus: Theodoxus Montfort, 1810
        Subgenus: Neritaea Roth, 1855
Genus: Vitta Mörch, 1852 (11 species)
        Subgenus: Vitta Mörch, 1852
        Subgenus: Vitoclithon Baker, 1923
Genus: Vittina Baker, 1923 (18 species)