234 PORINIDJE. 



fully stellate character. Calcification is carried to a great 

 extent in this species ; and the walls become very thick and 

 solid, and rather coarse in appearance, as we might ex- 

 pect in a deep-water form. It is often difiicnlt to deter- 

 mine the nature of the pore on the front of the neck-like 

 prolongation of the cell. In the older zooecia it is usually 

 a simple circular opening of rather large size ; but in the 

 younger it shows its true character, and is covered by a 

 pointed avicularium. The smaller pore on the upper 

 margin, which is sometimes very conspicuous, is also avicu- 

 larian ; but the appendage itself is very generally wanting ; 

 when present, its mandible is directed downwards. 



There is considerable variability in the shape o£ the 

 orifice, which seems to be chiefly due to the thickening of 

 the peristome with age. 



Habitat. On stones, shells, Gorgoniae, &c., from deep 

 water. 



Locality. Shetland, on shell (Barlee) : ibid., common 

 in 80-170 fathoms (A. M. N.). 



Geographical Distribution. North Sea, off Norway, 

 on Gorgoni<2 and stones from 200-300 fathoms (Baron 

 Uggla) : W. off" Tortugas (Pourtales). 



In A. monodon the zooecia are distinct, but separated by 

 shallow sutures, and very slightly convex, so that the 

 zoarium has a flattish appearance. The stellate character 

 of the punctures with which they are thickly covered, is 

 hardly apparent except in young specimens. The oral ex- 

 tremity is slightly tiuned upwards ; and the mouth is girt 

 about with a massive peristome : the pore in the centre of 

 the upper margin is the '^ tooth "which suggested the spe- 

 cific name. 



At the base of the cells there is a row of circular 

 openings. 



