sklered the pedal, adzocvcial chamber ol' the iiiolher-zooeciuiii, being situaled on 

 [he proximal surface of Ihe respective lateral wall, through the rosette-plates of 

 which it is in direct comnuinication with the zod'cium. The infra-scapular cham- 

 ber of the mother-zooecium is wanting. 



At a certain age an occlusion of the aperture gradually takes place (PI. XI, 

 ligs. 1 o, 1 p), and the calcareous lamina which fills it, the oral cryptocyst, joins 

 a cry[)tocyst expansion developing on the inner side of the slernal area and 

 taking its origin from the outer part of the single feneslrte. In contrast to the 

 several times mentioned, rounded cryptocyst lamina, the sternal cryptocyst, we 

 may call this the marginal cryptocyst. After having reached a certain size the 

 cryptocyst lamina; of the single fenestrje unite together and with the oral crypto- 

 cyst by means of a connective ridge formed across the inner surface of each 

 sternal rib, and henceforth the marginal and the oral cryptocyst form a continu- 

 ous ring-shaped expansion, gradually increasing in breadth. The oral cryptocyst 

 i.ssuing from the junction of the horizontal and the obliquely ascending parts of 

 the distal wall is directed proximally and frontally and increases in extent simul- 

 taneously with a considerable increase in thickness on account of new calcareous 

 layers being formed on its frontal surface. The sternal cry|)tocyst gradual!}' coa- 

 lesces not only with the ribs but on both sides of these also with the outer 

 (fenestral) jjarl of the marginal cryptocyst and this may lead to a complete oc- 

 clusion of the fenestrse. 



Setting aside the fact that from the daughter-zooecium of the bizocecial inter- 

 node a number (up to 4) of successive, single zooecia may sometimes arise, the last 

 of which completes the branch, the uni- and bizocecial segments otherwise alter- 

 nate regularly in this species. With regard to the position of the separate zoa>cia 

 we must notice, that the mother- and daughter-zoa^cium of the same segment 

 have the acute-angled corners of their respective apertures directed towards each 

 other, and the position of thg apertures of the succeeding single zocecia is the 

 same. The above-mentioned, successive single zooL'cia all have the apertures situ- 

 ated in the same way, whereas the aperture of the mother-zoa'cium in the bi- 

 zoaH"ial segment has an inverted position in relation to the lower zoa'cium. The 

 lateral branches, which always arise from the daughter-zoo'cia, spring alternately 

 from the right and the left side. 



For the sake of completeness I must further add that the colony is provided 

 with radical fibres, which form close bundles along the basal side of the separate 

 branches and spring from the basal side of the zorecium with which they 

 communicate through a collection of numerous uniporous rosette-plates. 



OcEcia are wanting in the colonies from the Bass' Strait, to which the above 



15 



