616 Scientific Proceedings, Royal Dublin Society. 



is a spine with a vertical branch bearing an avicularium with a 

 long curved pointed mandible, and with a horizontal bifurcating 

 branch arching over the area. At the oral end of the cell are two 

 vertical bifurcated spines. 



The radical tubes are present in this variety, but not in such 

 abundance as in the typical form of the species. Some of the cells 

 are quite destitute of processes giving origin to radical tubes. 



The zooecia are packed close together, so that the probable 

 original separation of the cells would never be suspected. 



In a valuable collection of the Polyzoa of Port Phillip, pre- 

 sented to the Natural History Museum by Mr. Bracebridge Wilson, 

 is a specimen of Membranipora radicifera} The radical tubes form 

 a thick felt- work. In the same collection is a specimen of Hianto- 

 pora ferox, Mac Grillivray. 2 The variety of M. radicifera, from 

 Torres Straits, is evidently a form intermediate between Membra- 

 nipora radicifera and Hiantopora ferox. In the latter the spines 

 have undergone further development; the horizontal portion on 

 the avicularian side of the cell has grown over the whole area, and 

 fused with the opposite cell margin. 



The resemblance between Cribrilina ferox and M. radicifera, 

 with regard to the presence of radical tubes and the disjunct 

 arrangement of the zooecia, was observed by Mr. Hincks. 1 The 

 discovery of the intermediate form from Torres Straits was neces- 

 sary in order to show the intimate relations between two such 

 diverse forms as M. radicifera and C. ferox. Viewed by itself it 

 may have been justifiable to place the latter form in the genus Cri- 

 brilina, or to make a new genus, Hiantopora ; but in view of its 

 relationship to M. radicifera, this can no longer be done, unless 

 the slightly increased development of spines (in this particular 

 instance) is to be considered a generic character. 



The following arrangement is proposed : — 

 Membranipora radicifera, Hincks. 



Membranipora radicifera, Hincks, var. intermedia, nov. var. 

 Membranipora radicifera, Hincks, var. ferox. 



1 Hinck's " Ann. Mag. Nat. Hist." (5) vin., 1881, p. 5 and 7., PI. II., figs. 6, 

 6a, 6b. 



3 Mac Gillrvray, " Cat. Mar. Pol. Vict.," p. 22; "Prod. Zool. Vict.," Decade X., 

 p. 34, PI. XXXVIII., fig. 8. ; "Prod. Zool. Vict.," Decade XII., p. 69, PI. CXVII.^ 

 figs. 6-8. 



