(JouRN. R. MiCR. Soc, 1910, pp. U2-113) 59 



V. — Note, on Dendrohnwhla fallax Brook, a Rare and 

 Scmarkahk Antipatharian. 



By Professor J. Arthur Thomson, M.A. 



(Bead Fcbmarij 16, 1910.) 



In a collcctidii of Alcyoii;irian.s wliicli 1 received for description 

 from His Soreue Highness the Prince of Monaco, there were four 

 specimens of unusual appearance and puzzling character — with a 

 spinose axis and pinnate tentacles — wliich are undoubtedly refer- 

 able to a remarkable type of Antipatharian, which llrook described 

 in ]8S'.I under the name Dcadrohrachia fallax. Although I have 

 not much that is new to add to Brook's excellent descrijjtion and 

 figures, it may be of interest to record the re-observation of an ex- 

 traordinary type, which seems to have remained unnoticed for more 

 than twenty years. Very unfortunately, three of the specimens 

 were dry, while the fourlli, which was preserved inspirit, had only 

 a few extremely brittle polyps. 



What are the peculiarities of the type wliich give it a somewhat 

 aloof position among Antipatharians ? 



1. The axis is without a central canal. In its younger parts it 

 consists of about five longitudinal ridges or plates, standing out 

 from a thin central stem and showing a distantly dentate margin. 

 As growth goes on, there seems to be an increase in the number of 

 outstanding ridges, and at the same time, by the deposition of 

 successive concentric layers of horn, the deep troughs between the 

 ridges are filled up, and an apijroximation to the ordinary type of 

 Antipatharian axis is thus reached. There is great diversity in the 

 size and .shape of the spines in different parts of the colony. The 

 colour of the axis varies from yellowish-brown to amber-brown. 

 The basal portion, which was ab.sent in Brook's two specimens, is 

 well seen in two cases. 



2. The iiolyps are even more remarkable than the axis. They 

 arise laterally, often in sub-opposite pairs, but there may be a con- 

 sidcralile interval, of two lengths or more, between two pairs. In 

 short, they are much more distant than is usual in Anti]iathariaijs. 

 Nor do they, in most cases, stand out at right angles, as Antipa- 

 tharian polyjjs usually do ; they are often appressed to the twig, or 

 form an acute angh> with it. The tentacles are retractile, which is 

 also unusual, so tliat in some cases there is simply a circle of knobs 

 around the prominent oral cone. StUl more striking is the fact 

 that they bear well-developed pinnules, six to seven pairs in the 



