Sich and Chard made such charming cut-ups I almost forgot how unenjoyable this story had been for me.
I looked on the internet for "Madame Demers." Here's the autopsy of my research (for less than an half-hour I believe):
1. Demers can be spelt all manner of ways and can even be De la Mare.
2. The highest concentration of Demers in the United States is in Massachusetts, there are a large number in Quebec and there are branches in Louisiana. The name is thought to have originated in Normandy and there is a Demer River in Belgium.
3. Lovecraft was likely making reference to a little known "Demers Affaire":
Le 13 juin dernier, jour de la Fete-Dieu, on decouvrait dans une maison de la rue Notre-Dame, sur le territore de Saint-Henri, le corps d'une femme a demi-vetue, etendu sur le sol de sa chambre, portant au cou deux entailles epouvantables.
Au priemier examen, on crut a un suicide. Tout plaidait en faveur d'une mort volontaire : le bon ordre qui regnait dans l'appartement, le silence qui avait enveloppe le drame, la taciturnite habituelle de la defunte.
L'impression premiere fut, pour tout le monde, que la femme Demers, dans un moment d'aberration communa a toutes les jeunes femmes nevropathiques, avait mis fin a ses jours en se coupant la gorge.
Mais lorsque l'autorite judiciare, representee par le coroner MacMahon, eut constate l'absence de tout instrument susceptible d'avoir servi a la desesperee pour l'accomplissment de son acte ; lorsque ce magistrat fut oblige de reconnaitre que la femme n'avait pu derober aux recherches de la justice l'instrument meurtrier en le faisant disparaitre, sout en le jetant par la fenetre, soit en le plongeant dans la fosse d'aisances, soit de tout autre facon, il fallut bien ecarter l'hypothese d'un suicide et ne voir qu'un meurtre abominable dans cetter mysterieuse affaire.
La victime, en effet, reposait sur le sol inonde de sang, mais nulle trace sanglante n'etait apparente dans le voisinage du cadavre. Preuve sans replique que la malheureuse n'avait pu faire un mouvement apres avoir recu les coups qui avaient entraine sa mort.
Il y avait donc un criminel, et un criminel que l'on ne pouvait rechercher parmi les vagabonds ou les bandits qui penetrent dans les maisons pour voler, fut-ce au prix d'un meurtre, car on ne put constater la disparition d'aucun objet, meme de minime valeur. ...
From the preface by M. Henri Roullaud to Plaidoyer de M. O. Desmarais dans l'Affaire de Napoleon Demers. Report stenographique de A. St. Martin, stenographe officiel, Montreal 1896. Printed by Louis Belair.
4. While looking, wikipedia gave a false-positive and misdirected me to
http://en.wikipedia.org/wiki/Napoléon,_Prince_Imperial (I think because one of his relatives' titles was Queen of the Sea or something, not sure), this being the young Napoleon IV who fled to the UK and died in South Africa during a war against the Zulus there (the Zulu War of 1879). There is an asteroid named jointly after him and The Little Prince, called Petit-Prince. It is the first known asteroid moon of another asteroid. But the interesting part was here:
DeathOn the morning of June 1, the troop set out, earlier than intended, and without the full escort, largely owing to Louis's impatience. Led by Carey, the scouts rode deeper into Zululand. Without Harrison or Buller present to restrain him, the Prince took command from Carey, even though the latter had seniority. At noon the troop was halted at a temporarily deserted kraal while Louis and Carey made some sketches of the terrain, and used part of the thatch to make a fire. No lookout was posted. As they were preparing to leave, about 40 Zulus fired upon them and rushed toward them screaming
uSuthu!. The Prince's horse dashed off before he could mount, the Prince clinging to a holster on the saddle--after about a hundred yards a strap broke, and the Prince fell beneath his horse and his right arm was trampled. He leapt up, drawing his revolver with his left hand, and started to run--but the Zulus could run faster. The Prince was speared in the thigh but pulled the
assegai from his wound. As he turned and fired on his pursuers, another
assegai struck his left shoulder. The Prince tried to fight on, using the
assegai he had pulled from his leg, but, weakened by his wounds, he sank to the ground and was overwhelmed; when recovered, his body had eighteen
assegai wounds.
(i.e., "One day ye'll hear them calling their father's name on top of Sobuza's kraal..", although u-Suthu seems half Yog S. minus what would be the prefix *yog- in Bantu languages plus Cthulhu minus the suffix *-lhu in some proto-Amharic type language. Then again, maybe Lovecraft really meant to write Yog-Suffix, perhaps, or Yog-Sussex, but kept with his first rendering instead???

)
Oh, and I almost forget, the alleged Demers family crest:
