Six pearly nautili (Nautilus pompilius) raised in captivity produced nonviable egg capsules which were examined using scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS). Macro and microscopic observations revealed two distinct and separate walls encircled the yolk sac. Both walls exhibited a porous appearance in cross-section. Protein analysis demonstrated the proteinaceous nature of nidimental gland secretions and egg capsule walls. EDS analysis of each wall shows the elemental composition to be identical in both, with each wall containing similar proportions of S, Cl, Mg, Na, K, and trace amounts of Ca. X-ray mapping of Na and Cl along each wall surface suggests similar construction of both walls. EDS analysis of the nidimental gland secretions of the adult female nautilus have shown a composition similar to that of the egg capsule.