18 THE VOYAGE OF H.M.S. CHALLENGER, 



A somewhat similar structure is described by Mr. Busk in Siphonicytara, and they 

 should on this account be placed, at any rate, in the same family. 



Urceolipora dentata, MacGillivray, has a similar structure, and so has Calwellia 

 hicornis, so far as I can judge the latter from dried specimens, leading to the conclusion 

 that the correlation of aperture, pores, and ovicell in these species, shows that too much 

 importance has been attached to the form of growth. 



As to Flustra homhycina, I am in doubt ; but in the British Museum specimen there 

 is a projecting tongue (fleshy ?) projecting partly over the pore. 



Habitat. — Add Station 150, 150 fathoms. 



Genus Retepora. 



Since Mr. Busk's Report was written, a paper by MacGillivray, dealing with 

 Retepora, has appeared in the Zool. of Victoria, decade x., and as both were in print 

 about the same time, there is some overlapping ; so that now several of the names used 

 in the Report are changed, and probably others will be found to be only synonyms. 



Retepora frequently require calcining to distinguish all the structure, and by this 

 means round dorsal avicularia have been found on several species where they were said 

 to be absent. 



As far as I am aware, the embryology of Retepora has never been described, and as 

 the genus is one presenting many peculiarities, an acquaintance with its earlier stages is 

 much to be desired. 



Mr. Kirkpatrick informs me that a specimen in the British Museum, named Retepora 

 grseffei, Kirchenpauer, is the Retepora producta of Busk. As this is probably from the 

 Museum Godeflfroy, it may be the type specimen, but as the description is insufficient 

 the name must be dropped. 



The gland-like sacks found at the two sides of the aperture in many Reteporas are 

 referred to when describing the avicularia of Lepralia margaritifera. 



Retepora tesselata, Hincks, var. imperati, Busk (PL III. figs, 7, 8, 39). 



Retepora imperati, Busk, Zool. Chall. Exp., part xxx. p. 110, pi. xxvi. fig. 9. 



The operculum is quite similar to that of the typical Retepora tesselata from Australia, 

 and I am in doubt as to whether they should be separated as varieties. In Retepora 

 imperati the avicularian chamber is stouter than in Retepora tesselata, and there are 

 none of the gigantic avicularia. In some parts of the zoarium the ovicell is almost entirely 

 immersed. In both this and the typical Retepora tesselata there is a minute sinus in the 

 oral aperture. There are numerous strong calcareous radical processes ; but this is not at 

 all uncommon in the Reteporse, though Retepora columnifera of the Challenger seems to 



