Mr. T. Wlutelegge on Australian Pol^zoa. 17 



examination of this species that I have been enabled to work 

 out the structure of the others. The zoarium, when seen in 

 longitudinal section, shows the concave side as having a can- 

 cellated layer of varying thickness, from which the zooecia 

 take their origin ; each zooecium is narrowed at the base and 

 very slightly bent inwards ; its direction from this point is 

 outwards, with a gentle curve upwards at nearly right angles 

 to the cancellate layer. 



Wiien the zooecia are seen in transverse section the outline 

 of each zooecium is irregularly pentagonal. 



Tiie anterior pore, when seen from within, appeal's as a 

 flask-shaped projection on the cell-Avall, and is about as long 

 as the shorter diameter of the mouth ; in some there app?;ar3 

 to be an opening, and in others tlie base is well rounded, with- 

 out any opening ; it may possibly be the retreat of a protra- 

 sible sensitive organ, but in no case have I seen anything at 

 the upper extremity which would indicate the presence of an 

 external vibracular organ. The cancellate structure, which 

 exists more or less in all the species, may originate by the 

 lower portion of the zooecia being continually partitioned off 

 as the zoarium increases in size. 



In some of the specimens lent by Mr. Brazier the ooe^ia are 

 fairly abundant ; but, except wlien the zoarium is broken into 

 two halves or set on its edge, the orifice cannot be seen. 

 From this fact it will be evident that they are in the usual 

 position above the mouth and nearest to the primary part of 

 the zoarium. 



3. Bipora depressa (Haswell). 



Conescharellina depressa, Hasw* Proc. Linn. Soc. N. S. W. 1880, 

 part i. vol. v. p. 41, pi. iii. fig. 4. 



Zoarium biconvex, slightly flattened beneath ; oral aperture 

 elongate, rounded above, with a sinus below, about half the 

 diameter of the mouth ; or ovate, with a subtriangular den- 

 ticle on each side near the base. Operculum ovate, with a 

 very slightly thickened border and two circular spots on the 

 upper half; peristome much elevated above and on eacii side 

 to below the mouth, then suddenly depressed; an avicuUirium 

 with an elongate triangular mandible situated on a low eleva- 

 tion on one side of the mouth. 



" Under surface of zoarium perforated by close-set circular 

 pores, each occupied, either at the surface or at a varying 

 depth, by a thin translucent covering perforated by sev^eral 

 minute porules, usually with a rather larger one in the 

 centre." 



Ann. ii) Mag. N. llist. Ser. 6. Vol. i. 2 



