MEMBRANIPOUA FLUSTROIDES. 151 



position, and occur on the side of the cell (not on the 

 margin) in the neighbourhood of the first pair of spines 

 below the orifice. It is perhaps hardly necessary to add 

 that they bear no morphological relation whatever to the 

 spines. 



Membranipora flustroides, Hincks. 



Plate XIX. fig. 2. 



Membranipora flustroides, Hincks, Ann. N. H. Sept. 1877, ser. 4, xx. 

 213, 214. 



Zocecia large, in regular lines, set closely together, oval ; 

 margin with 12-14 massive, flattish, sometimes sub- 

 clavate, sometimes bifid spines, which bend inwards, and 

 almost meet across the area, with the exception of the 

 two uppermost, which stand erect ; an oval avicularium 

 on a somewhat quadrate area at the top of many of the 

 cells, slanting upwards, with a semicircular mandible. 

 Ocecia very small and inconspicuous, smooth, elevated 

 in front, forming a hood-like covering over the extreme 

 end of the cell. 



Colonies forming large subcircular patches with a some- 

 what lobate edge. 



Range of Variation. Very limited. The cells are occa- 

 sionally smaller than usual; and there are very slight 

 diff'erences in the number of spines. At times two avicu- 

 laria occur side by side ; and rarely one is met with ab- 

 normally large. When developed above an oviccll, the 

 avicularium is commonly placed transversely. With the 

 exception of such slight differences, there is a remarkable 

 constancy of character in this well marked and very in- 

 teresting form. 



Habitat. Stones, shells, &c,, from moderate depths 

 and from deep water. 



