18 Proceedings of the Royal Irish Acadnuij. 



section reveals the fact that the furrows correspond in position to the canals 

 of the inner longitudinal series. 



Consequently, since the number of these canals diminishes from the 

 base upwards, the number of ridges and furrows also diminishes, so that 

 the actual number of furrows seen at any one level is not characteristic 

 of the colony as a whole (see fig. 11a, h, and c). It is unfortunate, 

 however, that several authors have used the number of furrows as a character 

 on which to separate different forms ; for it is at once evident that such 

 diagnosis must be negatived. 



In some eaaes — perhaps in all — although it is not very marked, two of the 

 furrows are deeper than the others, and these correspond to the two large 

 canals. 



Thus, then, we see that the inner longitudinal series of canals has 

 several well-defined characteristics, two, at any rate, of which may with 

 safety be regarded as specific, namely : 



(1) A certain number, constant for the specimen, are decidedly larger 

 than the others. 



(2) These large main canals determine the distribution of the verrucae, 

 and manifest themselves externally by longitudinal bare tracts. 



For these reasons we have decided to use this character as a basis for 

 specific diagnosis. 



(3) Polyps. 



(a) Structure. — The polyps vary greatly in shape, not only in different 

 specimens, but also in different parts of the same specimen. The structure 

 is essentially simple ; fig. 1 of Scirpearia pectinata may be taken as typical. 

 (See also fig. 74 of *S'. furcata.) It consists of (1) the verruca, and (2) the 

 anthocodia. There is no distinct point of demarcation between the two, but 

 the one merges imperceptibly into the other. It may, however, be useful to 

 distinguish between the lower cup-like portion, which may be termed the 

 verruca, and the upper tentacle-bearing portion, the anthocodia. 



The verruca arises from the general coeuenchyma, but is supported by 

 spicules of a different type, as will be explained further on ; these have no 

 definite arrangement. Near the summit there are usually eight triangular 

 lobes or teeth which are also densely spiculose. From these arise the short, 

 stumpy pinnate tentacles ; these are usually very broad, conical in shape, 

 and bear short, simple pinnules about six to ten in number. 



The anthocodiae are usually white, no matter what may be the colour of 

 the colony, and the tentacles bear a number of small, fiat, scale-like spicules 

 on the aboi'al surface. These are very easily overlooked in a preparation ; 



