412 DR S. F. HARMER AND DR W. G. RIDEWOOD ON THE 



number, one to each ostium. They further differ in that they include shelly particles 

 (see text-fig. 3), although these are present to a less extent than in the general 

 substance of the ccenoecium. They are fairly pointed at the extremities, although the 

 actual shape may be the result of the size and form of the included shelly particles, 

 and they broaden out at the base and curve round the ostium for about one third of 

 its margin. In protected situations the inhabited tubes are seen to widen out suddenly 

 as they reach the surface, and resemble very short funnels, and it is from the rim of 

 the funnel that the lip projects. This accounts for the distance between the spine and 

 the tube in the surface-view of the branch shown in text-fig. 2, B. 



A careful examination of the outer surface of a piece of colony and a dissection into 

 the substance of the ccenoecium between the tubes reveals the presence of broken 

 spines in association with the several ostia, and leads to the conclusion that the whole 

 of the surface of the colony is in the natural state provided with short lips or spines, 

 but that, owing to the rough treatment which the specimens must have experienced in 

 coming up in the trawl with a great weight of other specimens, their surface has been 

 scoured and deprived of the projecting spines, which are now only to be seen in their 

 full development in protected situations between branches which have not been broken 

 apart, as in PI. 1. fig. 1. 



Of particular interest in this connection is the fact that although in C. agglutinans 

 the zooids do not live in isolated tubes, but in tubes forming parts of a common tubular 

 system, the single lip or spine to each ostium is in other known species of Cephalodiscus 

 only met with in species of the subgenus Idiothena (C. gilchristi, C. nigrescens, and 

 C. levinseni) and Orthoecus (C. solidus), whereas in the known species of Demiothecia 

 the .spines are multiple, four or five being present around each ostium in the case of 

 C. hudgxoni. for instance. 



The tubular cavities which open to the exterior, and in which the zooids occur, are 

 approximately 1 mm. across, and the average distance from the middle of the orifice 

 of a tube to the middle of that nearest to it is 3 or 4 mm., except at the free end of a 

 branch, where the tubes are more crowded. The walls immediately bounding these 

 cavities are composed of a thin layer of yellowish-brown coenoacial substance, much 

 tougher than the jelly-like albuminoid that fills in the intervals between the tubes and 

 makes the whole so compact. The tubes proper do not include in their walls any of 

 the foreign bodies that give to the coancecium of this species its characteristic appear- 

 ance ; but some of the shelly particles of the softer material of the coenoecium are so 

 tightly fixed to the outer surface of the tubes that in dissecting a branch the tubes are 

 liable to be torn in the attempt to remove the particles. 



The tubes in the outer part of a piece of colony are fairly uniform in diameter (one 

 millimetre), except at the junction of two tubes, where irregularities in shape and size 

 may occur. A longitudinal section of a branch shows that the peripheral parts of the 

 tubes are not set at right angles to the surface, but slope somewhat towards the free 

 end of the branch (see text-fig. 1, C). In the middle of the piece the tubes are very 



(ROY. soc. EDIN. TRANS., VOL. XLIX., 530.) 



