160 MEMBRANIPORID^E. 



one only is usually permanent, but occasionally a second 

 survives. When the ovicell is absent there is some 

 amount of irregularity in the number and position of the 

 avicularia; sometimes the mandibles are turned down- 

 wards, as is frequently the case amongst the Membrani- 

 porae under such circumstances ; sometimes only a single 

 avicularium is developed, which is placed crossways, or 

 in the centre, with its mandible pointing straight down- 

 wards. This very distinct form has probably been con- 

 founded with M. Flemingii, which, as I have pointed out 

 elsewhere, has had a character for inconstancy which it 

 bv no means deserves. 



MEMBRANIPORA IMBELLIS, Hincks. 

 Plate XX. figs. 1, 2. 



MEMBRANIPORA IMBKLLIS, Hincks, Quart. Journ. Micr. So. viii. (1860), 275, 

 pi. xxx. fig. 1 ; Devon & Cornw. Oat., Ann. N. H. ser. 3, 

 ix. 28 (38 sep.) : Norman, Shetland Polyzoa, Rep. Brit. Ass. 

 1868, 305. 



Zocecia large, pyriform, contracted above and much ex- 

 panded below ; covering of the area wholly mem- 

 branous ; margin crenate or coarsely granulated, 

 thickened, especially at the bottom of the cell, where 

 it is usually somewhat produced and pointed. Ocecia 

 very prominent, frosted, with a depressed somewhat 

 quadrate area in front. No spines or avicularia. 



RANGE OF VARIATION. There is very great constancy in 

 the leading characters. The cells differ to some extent in 

 shape and size, and occasionally assume a subtriangular 

 form. 



HABITAT. On shells, stones, &c., from deep water. 



LOCALITIES. Coast of Antrim (Hyndman) : Scotland, 



