De Lapide Philisophico
This was a work which Joseph Curwen kept in his library in Salem. It is supposedly written by Trithemius who is also mentioned as the author of the Poligraphia, which Armitage consulted at Miskatonic University's library.
As for this work attributed to him by Lovecraft, we have found no reference to Trithemius having written it but there is a volume under the title "Lapis Philosophicus seu commentarius in 8' Lib: phys: Aristot: in quo arcana Physiologiae examinator" was written by John Case and published in 1599.
("The Case of Charles Dexter Ward," "The Dunwich Horror," "The Evil Clergyman")
See also: Trithemius and Poligraphia