20 



vessel; the superior or distal edge evenly rounded or curved; the proximal edge truncated, 

 and both the side edges or partitions only slightly convex, often nearly straight, erect or 

 prominent over the surface of the anterior side, which is flattened and smooth. These par- 

 titions are calcareous, strongly marked, and shew themselves as narrow hands of nearly opaque 

 white color. 



All formation of thorns or bristles is wanting on the cells. Close below their distal 

 border lies the opening, in the form of a transversal half moon- or crescent-like fissure, the 

 membranous lid of which sometimes appears raised, and in other cases closed. 



What is most remarkable in the present species is its avicularia: they are both in 

 size and shape similar to the cells. On closer examination they appear (see fig. 25 a) to be 

 about of the same width as the cells (sometimes, especially in the distal part, even a little 

 wider) but always a good deal namely V 3 1 / 2 longer (or iy 3 iy 2 millimetre, long and V 2 

 millimetre wide) as their proximal part forms an acute angle, while they are otherwise exactly 

 of the same shape as the cells. 



They are sparingly and pretty regularly or uniformly distributed over the whole colony; 

 their number is therefore considerably (about 7 9 times) less than that of the cells. They 

 appear always as a beginning to one of the two longitudinal rows, into which an elder row 

 of cells resolves itself in its accrescence. The r>i<tiutil>k> occupies the whole of the anterior 

 side of the avicularium, excepting the lately named lower part terminating in an acute angle, 

 which is occupied by the reccpfacidum, or that part of the avicularium, or the special cell (if 

 one prefers to call it so) which lies behind or below the articulation of the mandible, and 

 encloses the muscular apparatus for the movement of the mandible. This articulation is 

 formed by the distal extremity of the receptacle, a transversal straight line or border (one 

 side of the triangle) whereon the basis of the mandible, which also forms a transversal straight 

 line or border, is movably inserted. In dead colonies where the mandible has fallen off, there 

 is found in the place where it had been attached, namely close above the articulation, an 

 eliptical cavity in a longitudinal direction occupying nearly V 3 of the length of the avicularium, 

 as also instead of the receptaculum there is a large triangular cavity corresponding to its 

 outline. The anterior side of the receptacle is flattened, but the anterior side of the proper 

 avicularium is evenly convex or vaulted, and projects therefore considerably over the surface 

 of the colony formed by the cells. This convexity is caused only by the mandible, which when 

 lowered, exactly and closely covers the proper avicularium or cell ; but when the mandible is 

 raised, it shews itself to be entirely coincident with the cell, having the same size and shape, 

 namely the anterior side flattened, the distal edge curved, the proximal truncated, and both 

 the side-borders (partitions) projecting and calcareous like small white stripes. 



From what is already stated it will appear that the mandible in the F. abyssicola, 

 is, like the cells, of an elongated tongue-shape, but with convex or vaulted exterior surface 

 (the anterior side). Its opposite or interior surface is on the contrary strongly concave ; and 

 consequently the mandible is somewhat thin, and resembles the bmvl of a spoon. 



