Apertis thesauris*

Marginalia: 
A
Folio: 
041
Sequence: 
12
Office/Mass: 
V2
Genre: 
A
Position: 
4M
Cantus ID: 
001447
Mode: 
*
Manuscript Reading Full Text (standardized spelling): 
Apertis thesauris*
Manuscript Reading Full Text (MS spelling): 
Apertis thesauris. Salvum me fac. Usquequo domine. Dixit insipiens
Indexing notes: 
"Ad M"-why are these chants being placed in Matins-or does this abbreviation have another meaning?