120 Eev. T. Hincks's Contributions towards a 



an incrusting form, both fossil and recent, assumes the habit 

 of Vincularia on the coast of Australia. It also occurs, ac- 

 cording to this writer, (at Port Darwin) in an Escharine and 

 Hemeschariue form, as well as incrusting*. We have, then, 

 the same type of cell, and that a very rernarhahle and charac- 

 teristic one, associated with the Vincularian habit [S. Neo- 

 zeJanica)', with the crustaceous and Escharine habit [S.magni- 

 lahris) ; and with the Hemeschariue habit {S. Siuittii). And, 

 further, we have this type of cell combined with all these 

 modes of growth (according to Goldstein) witliin the limits of 

 a single species {8. Smittii). 



The significance of these facts will be more fully appreci- 

 ated if we consider the remarkable structural features of the 

 cell which is common to V. Neozelanica, Busk, and j\[emlrra- 

 nipora magnilahris, Busk. The chief character on which the 

 genus Steganojporella, mihi (which embraces them both), is 

 based, is the bithalamic condition of the zooecium.' Some 

 way below the uj^per extremity of the cell a diaphragm 

 shuts off the lower portion of the cavity, and forms a distinct 

 chamber for the polypide. A tubular passage (PI. V. fig. 8 a) 

 extends upwards from this chamber, and opens (in the two 

 species before us) into the upper chamber, which is always 

 large, and, in certain cells, of very ample dimensions ; in the 

 latter it ])robably represents the external ooecium of other 

 forms. Tlie opening of this chamber is closed by a very large 

 operculum, Avhich also protects the entrance to the tubular 

 passage through which the ])olypide issues. In the calca- 

 reous lamina covering the area there are two foramina, one 

 on each side, which open into the ujjper chamber. In the two 

 forms under consideration a screen-like denticle, deeply concave 

 in front, rises from the edge of the tubular passage, and occu- 

 pies the middle of the lower margin of the orifice. In the 

 perfect state an opaque membrane extends from the base of 

 the operculum to the bottom of the cell, a space intervening 

 between it and the calcareous lamina. A glance at the figures 

 (PI. V. figs. 8, 8 a, and 9, 9 a) will show tlie exact simihirity 

 between the two forms in all essential points ; they are also 

 curiously alike in some of the minute details. It is impos- 



* " Some neAv species of Bryozoa from tlie Marion Islands, with Notes 

 on BiceUaria grundis^'"' by J. li. Y. Goldstein. I have only a separate 

 copy of this paper (for which I am indebted to Mr. Goldstein's courtesy), 

 and am unable to give a more specific reference. The author considers 

 the changes of habit in <S'. Smittii to be " a sort of niimetism," and he 

 proposes to show " the importance of true zoarial habit as distinct from 

 mimetic changes of form." I am not sure that I rightly apprehend the 

 writer's meaning in this passage, and must be content to wait for a fuller 

 statement of his views. 



