MEMBUANIPORA FLE:MINGII. 163 



versely. Ocecia globose, commonly with a raised line 

 or rib forming an arch across the front of it, and 

 inclosing a minutely granulated area. 

 Primary cell small, circular, with a membranous cover- 

 ing, and eight or nine erect spines round the margin. 



Range of Variation. I believe, as I have said else- 

 where, that this species has been credited with a much 

 larger amount of variability than it really exhibits. Many 

 of the forms referred to it which diverge most widely from 

 the normal type are in fact distinct species. Its most 

 remarkable variations are due to age, and the consequent 

 loss of characteristic structures. 



Habitat. On shells, stones, Algse (more rarely), &c., 

 from between tide-marks to deep water. 



Localities. Very common and widely distributed. 



Geographical Distribution. East Greenland (Kirch- 

 enpauer, N. Germ. Pol. Exped.) : Gullmaren (Smitt) : 

 Adriatic, on mussels, Algse, and corals (Heller) : Roscoff, 

 common on Escharafoliacea (Joliet). 



Range in Time. Scotch Glacial deposits (Geikie) : 

 Palaeolithic ; clays of Western Scotland, &c. (A. Bell) . 



In fully developed specimens, in Avhich the cells are 

 crowded together, their real shape is scarcely apparent. 

 The area seems to occupy the whole of the front ; but, in 

 fact, the cell is produced to a greater or less extent below 

 it ; and it is on this produced portion that the a\icularia 

 are situated (Plate XXL fig. 2) . The zooecia are con- 

 tracted above, swell out in the middle, and then narrow 

 off towards the lower extremity. The area follows the 

 shape of the upper portion of the cell, and is narrow at 

 the top and very broad below. It is also much elevated 

 towards the bottom, so that the margin surrounding this 

 portion of it stands out very prominently. The spines 



M 2 



