STIMULATED by the findings of Young and Inman1 and Brown2 that the capsule of salmonid eggs can be classified as a pseudokeratin, we have recently made X-ray studies of the egg membrane of the brook trout, Salvelinus fontinalis. The membrane from the fresh unfertilized egg was washed with Ringer's solution to remove traces of egg contents and dried at room temperature. For analysis a Laue-type diffraction camera was used, with a flat film cassette 4.8 cm. from the specimen. The diagram obtained with copper Ka radiation, either vertical or parallel to the surface of the dry specimen, was a continuous halo with two main peaks at about 4.5 A. and 13 A. respectively (Fig. 1). As is also seen in Fig. 1, there is a sharp ring surrounding the whole halo. However, examination reveals that this ring coincides with the strongest line of sodium chloride, 2.81 A., and is wholly lost from membranes which have been washed with fresh water prior to desiccation. Consequently, it may be assumed that this ring pattern is not characteristic of the egg membrane, but is merely caused by adherent crystals of sodium chloride from the washing medium.