On sediments, from continental shelf to abyss.
Original taxon: Helonyx jeffreysi.
Dredged at 450m deep, Calvi Bay, NW. Corsica. 3mm.
« Shell somewhat spindle-shaped, proportionally broader (especially in the middle) than in any species of Siphonodentalium, nearly straight on the inner or ventral side, and gibbous or arched on the back, becoming suddenly contracted towards the base, where it is much narrower than at the top, very glossy and transparent. Sculpture: none. Mouth roundish-oval. Base flexuous, having two slight curved notches, one on each side; the very young shell has a projecting laminar process at the back. »
« Helonyx Jeffreysii. = Cadulus subfusiformis Jeffr. (non Sars). Apertura anteriore obliquamente troncata; base o apertura posteriore compressa, leggermente intaccata a ciascun lato. » – T. A. di Monterosato: “Nuova rivista delle Conchiglie Mediterranee”, Atti dell’Accademia Palermitana di Scienze… nuov. ser. vol. V, Palermo 1875.
The picture above shows the species in Pilsbry & Sharp: Manual of conchology ser. I, vol. XVII, Philadelphia 1897.
Finally: « The species described by Dr. Jeffreys as C. subfusiformis in the Appendix to British Conchology was afterwards stated by the Marquis de Monterosato to be not that species, and he re-named it Helonyx jeffreysi. Cadulus of Philippi is, however, prior to Helonyx of Stimpson, and the former generic name prevails. » – J. T. Marshall: “Additions to British conchology”, The journal of conchology vol. VII, London 1893, via BHL. – The shell differs from that of true subfusiformis by its more constricted extremities, and a more inflated shape. Nota bene that one ‘i’ disappeared from the epithet jeffreysii given by Monterosato.
