Upper side of seashell Neverita didyma (Röding, 1798)
[1], the bladder moon. Species from W. Pacific and Indian Ocean. Specimen collected in Philippines. ABBOTT, R. Tucker; DANCE, S. Peter (1982). Compendium of Seashells. A color Guide to More than 4.200 of the World's Marine Shells. New York: E. P. Dutton. p. 102. 412 pp.
ISBN 0-525-93269-0