Neoplanorbis

The genus Neoplanorbis includes the following species:

• † Neoplanorbis carinatus Walker, 1908^[3]
• † Neoplanorbis smithii Walker, 1908^[4]
• † Neoplanorbis tantillus Pilsbry, 1906^[5] the type species
• † Neoplanorbis umbilicatus Walker, 1908^[6]

Genus Neoplanorbis was originally described by Henry Augustus Pilsbry in 1906.^[7]

Note that Pilsbry described the shell as if it were dextral, whereas planorbids are now known to be sinistral in shell coiling. In other words what Pilsbry describes as the "impressed and turned in" apex of the shell is actually the center of the umbilicus.

Pilsbry's original text (the original description) reads as follows:

Genus NEOPLANORBIS n. gen.

The shell is minute, subdiscoidal, nearly flat above, convex below, perforate, carinate at the periphery, composed of about two rapidly enlarging whorls, the apex impressed and turned in. The aperture is very oblique, wider than high, a little dilated at the base. Peristome thin, not continuous, the columellar margin straight and broadly dilated, somewhat thickened within.

The dentition and so far as known, the soft anatomy, is similar to Amphigyra.

Type N. tantillus.

The type of this group was at first taken for a Planorbis of the P. dilatatus group, (It was reported as Planorbis tantillus in Mr. Hinkley's list, Nautilus XVIII, p. 54.) but when the dentition was examined it became obvious at once that the snail could not belong to the Planorbinae. The radula is not materially unlike that of Amphigyra, but the conchological features of the two groups are quite diverse, Amphigyra being Crepiduloid with a distinct "deck" or columellar plate, while Neoplanorbis is Planorbis-shaped, perforate, with a carinate periphery and no "deck."