subgrundarium

suggrundārĭum ( subg- ), ii, n. [suggrunda], the grave of a child less than forty days old (which was a niche in a wall, covered by a projecting roof or eaves; cf. columbarium, 2. d.): suggrundaria antiqui dicebant sepulcra infantium, qui necdum XL dies implessent, quia nec busta dici poterant, quia ossa quae comburerentur non erant, nec tanta cadaveris immanitas, quā locus tumesceret. Unde Rutilius Geminus Astyanacte ait:

Melius suggrundarium misero quaereres quam sepulcrum,

Fulg. Expos. Serm. Ant. p. 560.