22 THE VOYAGE OF H.M.S. CHALLENGER. 



Retepora magellensis, Busk (PL III. fig. 5). 



Retepora magellensis. Busk, Zool. Chall. Exp., part xxx. p. 126, pi. xxxvi. fig. 20. 



There is on the zocecium, about the middle, an avicularium with semicircular 

 mandible, and on the dorsal surface there are also similar avicularia and divisional lines. 

 These are distinctly seen when calcined, but otherwise may be overlooked, and no doubt 

 this accounts for Mr. Busk's description " without vibices or dorsal avicularia." This corre- 

 sponds in the zooecial characters with Retepora simplex of the Challenger, but that name 

 must be dropped, as Mr. Busk had already used it in his Crag Polyzoa. As Retepora 

 simplex seems to be only a slender form, I should propose that it be distinguished as 

 Retepora magellensis, var. minima. The variety minima has similar oral and surface 

 avicularia, but the zooecia are only about half as long as those of the variety typica. 



Turritigera stellata, Busk (PL L figs. 22, 25). 



Turritigera stellata. Busk, Zool. Chall. Exp., part xxx. p. 130, pi. xxiv. fig. 1. 



The end of the zooecial tube is closed by a calcareous layer, reminding us of the 

 closure of the Cyclostomata. In one case there is a prolongation of the zocecium, formed 

 by a plain narrow tube extending beyond the circle of avicularia, in another case sections 

 show the calcareous closure to be double, but usually it is only single. When looking at 

 the specimen in Edinburgh, I considered that the aperture was Schizoporellidan, but the 

 piece brought away having no opercula, I have been unable to confirm the observation. 



The inflation of some of the zooecia, referred to by Mr. Busk, is an ovicell, as may be 

 distinctly seen in sections. 



Cribrilina latimarginata, Busk (PL I. figs. 11, 12). 



Cribrilina latimarginata, Busk, Zool. Chall. Exp., part xxx. p. 131, pi. xxii. fig. 10. 



A specimen from the Edinburgh duplicates has numerous large vibracula, and they 

 are also well preserved in a specimen which I found at the British Museum among some 

 duplicate material, and this is the only Cribrilina in which vicarious vibracula are 

 known. When the vibracula are removed, a bar is seen extending half across the " large 

 suborbicular opening." The vibraculum has a process at one side of the base, and this is 

 situated below the bar, with one muscle attached to it and two powerful ones higher up. 

 I have elsewhere alluded to the unsymmetrical shape of the base of the vibracula, and to 

 this fundamental difi'erence between avicularia and vibracula. 



I do not find the flattened borders or bands as described by Busk, but, when calcined, 

 a thick calcareous growth is seen surrounding the area, leaving small triangular hollows 

 where the neighbouring zooecia meet, or nearly meet, and a thick membrane covers the 

 whole. The ovicell is not much raised, and has a triangular mark on the front. This is 



