Ancient examples:

 The site of Denkalelo in Djibouti, is tentatively dated to the 5^th millennium BP based on the presence of earlier pottery discovered there. Oyster shell debris was used to cover graves (Poisblaud et al. 2002). Poisblaud B., Bernard, R.,  Cros, J.-P., Dupont, C., and R. Joussaume. 2002. Le site de Dankalelo (Ghoubbet al Kharad, Djibouti). Annales d’Éthiopie XVIII:199-214.

Mulsim burials at Caesarea were covered with Glycymeris shells. Published in Caesarea papers 2 : Herod’s temple, the provincial governor’s Praetorium and granaries, the later harbor, a gold coin hoard, and other studies / edited by K.G. Holum, A. Raban, and J. Patrich. Portsmouth, R.I. : Journal of Roman Archaeology, Supplement 35, 1999.  (Sorry I don't have the book with page nos).

­Recent examples:

The custom of using oyster valves that were once food refuse to cover graves is practiced today in Senegal (Dioh et al., 2008). Dioh, E., Gučye, M., Diatta, Y. and A. Camara. 2008, Les différents types de gisements coquilliers dans la lagune de Joal-Fadiouth (Sénégal occidental). Paper presented at the workshop: Shell Energy: Prehistoric Coastal Resource Strategies, held in Dakar, Senegal, 8-11 April 2008. Organized by G. Bailey, K. Hardy and A. Camara.

At the Shiloh cemetery in Cedar Key, Florida, dated to the 18-early 20^th c.(?) there are Mercenaria sp. covering graves. See http://triton.anu.edu.au/Meeting.FL05.htm “Many of the grave mounds are covered with clam and other shells neatly arranged in rows. This unique feature is frequently seen in cemeteries in the Cedar Key, FL, area. In addition to being a decorative tradition, shell coverings were done to keep rain from washing the sand away from the grave mounds. Many of the gravesites are noticeable only because of a scattering of shells.” http://files.usgwarchives.net/fl/levy/cemetery/shiloh.txt Website accessed 29 Aug. 2011.