129 



calcified outer and a more slightly calcilied inner (median) part. The distal wall 

 is acute-angled and the two arms are a little concave. As in the loregoing species, 

 it is at the same time saddle-shaped, and furnished with a transverse row of 

 (up to 12) uniporous rosette-plates. The distal half of each side-wall has ca. 6 

 rosette-plates. The marginal region, which consists of kenozoo'cia, only differs from 

 the marginal region in the preceding species by the part, which ap])ears on the 

 basal side of the colony, being much calcified and furnished with similar stripes 

 to the zowcia. On the other hand, it has no distinct cryptocyst. The radical 

 fibres issue from the proximal corners of a number of fenestrse. 



Avicularia have not been found hitherto. 



The ooecia are high, dome-shaped, with indistinct radiating stria? and gener- 

 ally in the middle provided with a shorter or longer, sometimes rather irregular 

 ridge. A low cryptocyst belt covers their |)roximal part. Also here the basal part 

 of the distal wall lies higher than the top of the ocecium and is thus seen dis- 

 tally to the latter at a deeper level (PI. I, fig. 6 b, PI. XXII, fig. 2 a). The distal 

 wall belonging to the oa>cium forms an angular .or sometimes almost arched 

 mark on the basal side of the colony, and the two arms are not concave but 

 convex. The ocecia-bearing zoo'cia are, when looked at from the basal side, larger 

 than the others, and the distal half of the above-mentioned uncalcitied longi- 

 tudinal belt is generally very broad. 



The colonies have the same slruclure as in R. Sclwiuun, l)ut the fenestrje 

 are very much smaller and generally much narrower than the segments between 

 them. 



Of this species I have examined a fragment from Torres Straits (Cambridge) 

 and one from Port Darwin (Ihitish Museum). 



R. reticulum Hincks. 



Flustra reticulum Hincks, 



Annals Nat. Hist. .ser. o, Vol. X, 1882, p. 163, PI. YII, fig. 4. 



(I'l. XXII, lij^s. la-lc). 



The zooecia of rather varying form, most often irregularly pentagonal or 

 hexagonal with an evenly rounded frontal edge. A cryptocyst appears as an 

 extremely slight marginal expansion. The basal wall is uniformly, but not 

 strongly calcified with the exception of a rather small, round (circular, oval or 

 pear-shaped) uncalcified spot almost proximally to the distal wall. Very rarely 

 a few short, coarse stripes appear here and there. Contrary to the case in the 

 two other species the distal wall is generally straight in the ordinary zocrcia, 

 and it has about 10 uniporous rosette-plates, some of which are placed opposite 



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