Bythinella cebennensis (Dupuy, 1849)

Crenobiont. Known distribution: surroundings of Le Vigan and Ganges, Hérault, S. France.
Original taxon: Bythinia cebenensis. Synonym: ferussina var. “webbiana”.
There are two morphs: one, which matches the original description, has a noticeably lengthened spire; a second morph is much more stocky. Growth marks almost orthocline; whorls convex; subsutural ramp narrow; presence of an umbilical slit. Above and below: specimens of the first morph, collected in the pond of the Buèges river spring, Pégairolles-de-Buèges, Hérault.
Altitude ≈ 170m. Size of this shell: 3,5mm.

The shell of this morph can be almost as slender as that of the true ferussina (Des Moulins, 1827) from the Aquitaine Region. 3,75mm.

The second morph is often smaller in size, with a larger circumference, as it can be seen on the top of this picture: from left to right, morph 2 (2,75mm) - morph 2 (2,90mm) - morph 1 (3,30mm). Bottom: growth series in the second morph (left to right: 2,25-2,10-1,50mm). According to J. M. Bichain in his thesis, this morph corresponds to the Hydrobia eutrepha of Paladilhe (Jean-Michel Bichain: La systématique des bythinelles revisitée, Paris MNHN 2007, p.166-167 of the book).

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