Le Rongeur d'Os

One of the many phantom dogs is the "bone gnawer" Rongeur d'Os of Normandy, France. Considered a legendary Black Dog of doom, as well as loup garou werewolf, hell hound and chained demonic wolf who guards the gates to the underworld. In Cochraune's Foreign Quarterly, Issue 1, it makes a brief reference to the Rongeur d'Os as a very large spectral dog. It "wanders the streets of Bayeux" during the nights of Winter and chews on bones.

This phantom creature has chains around it and looks like the Yorshire barguest, another ghost dog. The dog Rongeur d'Os is not just a phantom but also a monster, for it gnaws on bones of dead animals and humans, wanders the city of Bayeux in Normandy, France, and frightens anyone that comes near it. The hound also emerges from the streets and roams the graves and countryside, snapping at any travelling passer by. The chain indicates a physical guard dog that was so commonly visible in France for the past thousand years. But this dog is a thing of the supernatural.

 In Norse mythology, Fenrir the giant wolf was chained. There are also tales of werewolves that developed in France during the Middle Ages. Some writers have indicated that Rongeur d'Os was a werewolf. Also in the same region of France is the legend of the female white spirits, Dames blanches, beautiful phantom maids in white who haunt footpaths, bridges, river banks, caves, hills and castle ruins. These could be identified as fae, Weisse Frauen, light elves or even Valkyries, as some suggest they're the Disir.

Associated with white ladies (ghosts) are the fearsome hell hounds and black dogs. Yet there are the less talked about phantom white dogs! These spectral demonic white dogs are always chained, and legends about these are found in England, Ireland and Wales and scattered parts of the European continent. France has the story that a werewolf, loup garou is a person who transforms into a white wolf. In Romania, gypsies believe white wolf ghosts linger around graves to destroy the undead and protect the living from stray vampires. The white wolves of Britain are the Cwn Annwn, nicknamed "fairy hounds", who have ruby red eyes. These dogs have been associated with the fae, death and the Wild Hunt. Cwn Anwwn appear in coldest Autumn and Winter nights.  

The northern area of France was much dominated by Viking descendants, the Normans, and stories of heroes, monsters and gods assimilated with the Celtic, Frankish and Gaulish legends.

Sources:
"Cochrane's Foreign Quarterly" (volume 1), by John George Cochrane.
"Beware of werewolf!" by Charles at Histoire Normande.
"Jersey Folklore & Superstitions" (volume 1), by G. J. C. Bois.
Myth & Beasts link.
Wikipedia Dames blaches.
Run with the Hunt link.
(At top is a picture by Max of a wolf with a dame blanche)