Mediterranean Live Shells, Help needed :)

[brunni]

Wonderful images ! I do not think any of them are Mitra nigra as it does not occur in the Mediterranean ( or France ). The dark shelled mitres of this area are very difficult to separate as shells. I think the most valuable comment on the subject has been :

ROLÀN, E., DANTART, L. & FERNANDES, F., 1997. On some dark species of Mitra from the Mediterranean and Atlantic. La Conchiglia, 29 (285), pp. 11-23

According to this you have 2 species in your images -
Mitra cornicula : animal all white
Mitra cornea  : white animal, broder with food with yellow band

In Mitra nigra the animal is crimson-brownand the base of foot cream-white.