374 MESSRS. E. HEEON-ALLEN AND A. EAELAND ON THE 



The protoplasmic body of India diaphana is large, filling the greater part of the 

 cavity even of the largest tests, and we figure an irregularly built specimen in which 

 the body of the animal has divided into lobes which extend into every part of the 

 " house " (fig. 9). In other instances, the protoplasm has contracted into a more or 

 less spherical mass (figs. 8 & 10) ; and it may be observed that, for such a large 

 organism, it is exceptionally free from inclusions, or metaplastic bodies, of any kind. 



None of the Kerimba specimens exhibits any definite papillee, such as were observed 

 in a few of the Bognor specimens. In young tests, as already noted, there is often a 

 simple aperture at the top or side of the dome, but this is not always visible. In the 

 larger specimens, one or more irregular apertures may sometimes be traced on the 

 surface of the test, but frequently there is no visible aperture at all, the organism 

 communicating with the surrounding medium by interstitial orifices of minute size, 

 situated among, and obscured by, the constituent particles of the shell-wall. 



As regards the primordial dome-shaped chambers, it is somewhat noteworthy that 

 both at Kerimba and at Selsey Bill these tests are usually found adherent to single 

 sand-grains rather than to larger fragments (PL XXXVI. fig. 1). We have re-examined 

 the Selsey Bill specimens, but have been unable to detect the presence of a chitinous 

 " floor " in any of them. At Kerimba, on the other hand, the chitinous floor appears 

 to be present in most (but not all) of the primordial tests (figs. 4 & 5), It may well 

 be that this final layer of chitin is usually formed and added at a late stage in the 

 life-history of the young domed shell. 



Iridia is unquestionably a very simple and primitive form of Rhizopod, but it is not 

 very easy to define its relationship to the other genera. In its sessile hemispherical 

 form, its chitinous lining, and occasional papillate processes it shows affinities to 

 the genera Thurammina and Wehhina with which it was originally classed, but the 

 aberrant and loosely constructed adult test is more suggestive of Astrorhiza, and it is 

 in the family of the Astrorhizidse that we consider that the genus should be placed. 

 Some of the large specimens from Station IX. are strongly suggestive of the central 

 disc of Astrorhiza limicola Sandahl, but lack the produced arms characteristic of that 

 species. The genus may be regarded as being to some extent isomorphous with 

 Nulecularia lucifuga Defrance. 



Iridia diaphana varies enormously in size, according to the stage in its life-history 

 and the conditions of growth. The earliest, or hemisj^hcej-ica-stAge, averages '25 to 

 •3 mm. at Kerimba, similar specimens from Selsey, being considerably smaller, 

 averaging "15 to •25 mm. Adult individuals show a great range in size even at the 

 same Station, but the general average at Kerimba ranges between "4 mm. and 1 mm-, 

 in greatest diameter of the test. The Bognor and Selsey specimens are of smaller 

 dimensions, but exhibit the same diversity of size. At Kerimba many specimens of 

 comparatively gigantic size were found, the largest being 8 mm. in greatest diameter. 

 These large specimens are usually of a narrow and elongate type. 



