Cranopsis: Shell height moderate; anterior slope broadly convex; apical whorl overhanging posterior slope; posterior slope concave; protoconch with linear and concentric sculpture; foramen on anterior slope of shell, its position in earlier growth stages marked by strong selenizone. Anterior slope in advance of foramen marked by doubled anterior rib and seam on interior surface. Foramen bordered posteriorly on inner surface by low, curved septum. Sculpture usually radial and concentric, radial sculpture marked by primary and secondary ribs.
Mantle skirt slit extending to position of foramen. Epipodial tentacles numerous. Ctenidia bipectinate, gill axis free.
Rachidian tooth usually narrow, inner lateral teeth narrow; pluricuspid tooth massive, with inner and outer secondary cusps.

Shell height moderate; anterior slope broadly convex; apical whorl overhanging posterior slope; posterior slope concave; protoconch with linear and concentric sculpture; foramen on anterior slope of shell, position in earlier growth stages marked by strong selenizone. Anterior slope in advance of foramen not marked by doubled anterior rib. Foramen bordered posteriorly on inner surface by low, curved septum. Sculpture radial and concentric, radial sculpture marked by primary and secondary ribs.
Mantle skirt intact anteriorly, perforated only to correspond to position or roramen. Epipodial tentacles numerous. Ctenidia bipectinate, gill axis free.
Rachidian tooth usually narrow, inner lateral teeth narrow; pluricuspid tooth massive, with inner and outer denticles.

Shell cap- or cone-shaped with oval aperture; apex rolled in backwardly and occasionally somewhat toward the right or reduced, as a rule with radial ribs and occasionally with fine granulations. A shell hole is present, as in Rimula: this is sometimes closer to the anterior margin, sometimes to the apex and can replace the position of the latter; correspondingly the slit band is longer or shorter or reduced; in contrast to Rimula, it is sunken under the surface chiefly with its anterior end.
The mantle of the animal may be anteriorly cleft or closed, a small projection may be elevated in front of the slit band; in the male, a penis is occasionally formed behind the right tentacle. Radula similar to that of Emarginula central plate somewhat longer than broad; outermost lateral plate large, fairly long and narrow; culling edge with pointed inner cusp.

Shell cap- or cone-shaped in most cases with smooth or tuberculate radial ribs; apex retained, hole close to it; slit band sunken like a septum, without distinct transverse folds.

Cranopsis: Shell cap-shaped with more or less large, rolled-in apex; surface with tuberculate ribs; hole situated in about the center between anterior margin and apex, anteriorly pointed, in young shells still open, in adults also showing the suture; slit band fairly long, with small transverse folds, anteriorly sunken. Mantle slit open; the epipodium is a narrow fold with a few small tentacles.

Type (OD) Patella noachina Linnaeus, 1758 Conical limpet-like shells, with a near summit perforation, the posteriorly recurved apical whorls persistent in the adult; perforation with an entering conduit, and within, a curved shelly plate or shelf; sculpture radially ribbed, and the colour usually white. Northern and Southern Hemispheres, in cold and cool temperate, shallow to deep waters; Eocene to Recent.

Cranopsis: Type species (M): Cranopsis pelex A. Adams, 1860. Japan.
Diagnosis. Anterior slope with interior and exterior groove or seam that extends from constricted lower end of foramen to shell margin. Groove located exteriorly between 2 closely adjacent ribs that form doubled, anteriormost primary rib; doubled rib deflected slightly toward right. Mantle skirt correspondingly split. Septum arched convexly, not supported by props.
Remarks. Earlier authors placed the Cranopis species in Puncturella Lowe, 1827, but the split mantle skirt of Cranopsis (described by Cowan and McLean, 1968) is unlike that of Puncturella Lowe, 1827, in which there is neither a split mantle nor a seam on the anterior slope of the shell, a distinction sufficient for the separate generic ranking of the two taxa.
Species of Cranopsis occur in both the northern and southern hemispheres, in shallow water at high latitudes and at greater depths at low latitudes.

Type species (monotypy): Patella noachina Linnaeus, 1771. Circumboreal.
Diagnosis. Shell conical, white; young shells with fine white punctations. Foramen on anterior slope, apex inclined toward right. Interior with forward-sloping septum separateing mantle cavity from visceral region; septum often flattened, supported by props; septum continuous with depressed selenizone originating just anterior to apex.
Remarks. Puncturella lacks the anterior seam on the shell and the split mantle roof that characterizes Cranopsis. The shells are also somewhat smaller than those of Cranopsis. Like Cranopsis, Puncturella species occur at high latitudes or in deeper waters at low latitudes in both the northern and southern hemispheres.

The distinction between Cranopsis and Puncturella s.s. has been made generally on the basis of the location of the anal foramen (Keen 1960; Farfante 1947). Other given characters such as the presence or absence of a selenizone, and of a groove on the interior from the foramen to the anterior shell margin, seem to be variable. Cowan & McLean (1968) stated that a more useful character was the presence in Cranopsis of a major double rib, produced by the split mantle, extending from the foramen to the anterior margin. This is certainly very clear in strongly ribbed species such as P.(C.) cucullata (Gould, 1846) and P.(C.) multistriata Dall, 1914, but is less so in smoother forms, such as P.(C.) serraticosta sp. n. Moreover the anterior rib in some typical Puncturella species (e.g. P. capensis) is broader than the others and may be shallowly bifid. It would seem that the most reliable features remain the position of the foramen and the degree of development of the internal septum, which is always much smaller in Cranopsis. Presence or absence of a split mantle is potentially useful, but has been investigated in too few species.