RHTNCHOPORA BISPINOSA. 387 



reduced in size, and flattish, the sutures disappear, and the 

 punctures mark out the boundaries ; under such circum- 

 stances the ovicell is completely immersed. The marginal 

 perforations are at times a very conspicuous character ; 

 but in many cases they are hardly distinguishable. The 

 young marginal cells are regularly ovate, perfectly smooth 

 and horizontal, with a somewhat transversely elliptical aper- 

 ture, very slightly sinuated below, and two slender spines 

 on the upper lip. At a very early stage a small central pro- 

 minence appears on the lower margin, which, increasing in 

 size, bends over to one side, and forms the uncinate process 

 to which reference has been made. A small denticle pro- 

 jects from the side of the orifice towards which it inclines ; 

 and the two processes, meeting, inclose a circular space. 

 Immediately behind this process, the foundations of the 

 avicularian swelling (or mound) are traceable on some of 

 the cells and in some colonies, while in others the suboral 

 mucro rises in the same position*. In the second or third 

 line from the edge the cells have generally acquired their 

 granular covering and their polished and glistening ap- 

 pearance. The small avicularia, which are much elevated, 

 are variable in number ; and two or three are frequently 

 met with on a cell. 



In sheltered situations the suboral mucro is much de- 

 veloped, and the surface of the zoarium bristles with long 

 spear-like processes. 



HABITAT. On stones and shells from shallow to deep 

 water. 



LOCALITIES. Berwick Bay, on Modiola (Johnston) : 

 South Devon, abundant ; Cornwall, off the Deadman, 60 

 fathoms; Guernsey (T. II.) : Shetland, 50-170 fathoms 

 (A. M. N.) : Caithness, very rare (C. W. P.). 



* This seems to be the normal position of the inucro ; it is, as it were, dis- 

 placed when the aviciiluriuni is present. 



2t2 



