This is the hard shell (or test) of a keyhole arrowhead sand dollar (*Encope grandis*). It is a member of the family Mellitidae and found in the Eastern Pacific Ocean along the coast of Mexico and California.
More info here:
https://www.inaturalist.org/observations?taxon_id=293119
http://www.marinespecies.org/aphia.php?p=taxdetails&id=513256
Accession number: 163.17
Captured with Artec Spider 3D Scanner
https://www.artec3d.com/portable-3d-scanners/artec-spider-v2