3*22 Proceedings of the Royal Irish Academy. 



The following notes on some of the aberrant specimens may serve to 

 give an idea of the inherent specific character : — 



II. One of the pi-imary branches has been broken off after a distance 

 of 28 cm. ; but the branch which arises nearest that point has developed 

 twigs on the inner side, and has so continued the general development 

 as if primary. 



VII. One of the primary branches, along with the first two secondaries 

 which arose from it, has been broken off; but the fourth has taken its 

 place, and continued the regular development of tertiaries just as if they 

 were secondaries. 



IX. One of the primary branches is only feebly developed, and has 

 six short slender secondaries. The second secondary has developed tertiaries 

 after the manner of a primary. 



X. A similar mode of development to that described for II. has taken 

 place in this specimen. 



Branching. — The branching of this unique type is extremely characteristic. 

 The main stem is usually very short, and gives rise to two branches dichoto- 

 mously ; these arise at varj-uig angles in the different specimens. In some 

 they lie almoet horizontally (fig. 36) ; in others they are inclined at 45° 

 (fig. 37), or even 60° (fig. 38), to the horizontal. In a typical specimen 

 these primarj' branches give rise to secondaries on the upper inner aspect 

 in a symmetrical manner, giving a distinct comb-like arrangement. The 

 angle at which these arise is ver)- characteristic. When colonies are preserved 

 in spirits or drietl, they usually contract, so that the secondary branches 

 overlap on eitlier side (fig. 39) ; but a study of these, when immediately taken 

 from the water, shows that this does not occur when growing freely. In this 

 condition all the secondary branches stand vertically, and arise from the 

 primary branches at an angle complementary to that at which the primary 

 branches arise from the main stem. Thus if the primary branches are 

 horizontal, the secondary arise at right angles ; if the primary branches arise 

 at an angle of 60' from the main stem, the secondary branches come of}' at 

 an angle of 30°. Stages between these are of course not infrequent. Fig. 3 

 shows the habit of a colony in the contracted condition, while figs. 36-38 

 show different angles of origin. 



Secondary complications sometimes occur in the branching, but it is 

 noteworthy that these tend to follow the tyjx? already described. For example, 

 in several specimens one of the primary branches has been broken off ; but 

 the secondary branch which arose at this point has developed tertiary 

 branches in a manner analogous to the primary branch (fig. 40). Occasionally 



