a General History of the Marine Polyzoa. 153 



comparable with the " serrated denticle," similarly placed in 

 Membranipora [Dijlustra) delicatula, Busk) ; and the mem- 

 branous portion at the upper extremity is only occasional, 

 and merely denotes imperfect development. That the true 

 upjyer loall of the zocecium is the membrane which closes in 

 the whole of the area is evident from the course of develop- 

 ment and from the fact that it bears the oral valve. In the 

 younger zocecia the laminar process is either wholly wanting or 

 very imperfectly developed, whilst the membranous wall, 

 furnished with the semicircular orifice for the egress of the 

 polypide, occupies the whole of the opening at a considerable 

 distance above the lamina. 



The real peculiarity of this form is that the membrane 

 incloses the granular plate and its process ; but this, how- 

 ever curious, is hardly a generic character. The same thing 

 occurs in a less degree in M. nitens^ mihi. As to the habit 

 of growth, MacGillivray's figure represents a small erect and 

 foliated specimen ; the one from Bass's Straits is wholly 

 crustaceous. Another which I have examined grows round a 

 stem of seaweed, and the free edges meeting on one side of 

 it come together and unite ; and in any further growth at this 

 point there would be a bilaminate structure, and the zoarium 

 would become erect and detached ; but it would be none the 

 less a Membranipora. The large nodules at the base of the 

 cells, which were present in the specimen I have figured, 

 materially change the general appearance of the species. 



Memh'anijjora cervicornis, Busk*. 

 (Ph VIII. fig. 1, and PI. X. fig. 3.) 



Zocecia oval ; margin much raised round the upper part of 

 the cell, forming a very thin wall, which also extends for 

 some distance down the sides ; area occupying the whole of 

 the front, about a third of it filled in by a smooth and shining 

 calcareous lamina, which is carried up for some distance on 



* There has been some doubt whether the M. cervicornis, Busk (Cat. 

 pt. 1, pi. c. tig. 3), is identical with the form described by MacGillivray 

 under this name. Busk's figure does not show the detail of the zocecium 

 very clearly ; but the branching spines, as he represents them, are cer- 

 tainly different from the similar appendages as given by MacGillivray. 

 They are massive and spreading, and bend in over the area, the branches 

 "meeting and inosculating;" whereas in the other form they are erect 

 and comparatively slender, and show no tendency to unite across the cell. 

 The colour also of Busk's species is said to be " pui-plish ; " that of the 

 Au' a-alian species white or brownish. Amongst Capt. Warren's dredg- 

 ings, however, from Bass's Straits, I have met with specimens undoubtedly 

 referable to MacGillivray's species, in which the spines are somewhat 

 more massive, and occasionally meet and (apparently) imite across the 

 cell J they are also of a deep purplish colour. 



