350 COELENTERATA ANTHOZOA chap. 



Gray; Zanzibar. Agaricoides, Simpson; 1 Indian Ocean, 400 

 fathoms. 



Order IV. Gorgonacea. 



This order contains a very large number of dendritic and 

 usually flexible corals occurring in nearly all seas and extending 

 from shallow waters to the very great depths of the ocean. A 

 large proportion of them are brightly coloured, and as the 

 principal pigments are fixed in the spicules, and are therefore 

 preserved when the corals are dead and dried, they afford some 

 of the most attractive and graceful objects of a natural history 

 museum. 



The only character that separates them from the Alcyonacea 

 is that they possess a skeletal axis that is not perforated by the 

 coelenteric cavities of the zooids. The coelenteric cavities are 

 usually short. The order may conveniently be divided into two 

 sub-orders. 



Sub-Order 1. Pseudaxonia. 



The axis in this sub-order consists of numerous spicules tightly 

 packed together, or cemented together by a substance which is 

 probably allied to horn in its chemical composition. This sub- 

 stance may be considerable in amount, in which case it remains 

 after decalcification as a spongy, porous residue ; or it may be so 

 small in amount, as in Corallium, that the axis appears to be 

 composed of solid carbonate of lime. The statement is usually 

 made that the axis is penetrated by nutritive canals in certain 

 genera, but the evidence upon which this is based is unsatisfactory 

 and in some cases unfounded. There can be no doubt, however, 

 that in some genera the axis is porous and in others it is not, 

 and this forms a useful character for the separation of genera. 



Fam. 1. Briareidae. The medullary substance consists of 

 closely packed but separate spicules embedded in a soft horny 

 matrix, which is uniform in character throughout its course. 

 Nearly all the genera form dendritic colonies of considerable size. 



The principal genera are : Solenocaulon, Gray ; Indian Ocean 

 and North Australia. Many of the specimens of this genus have 

 fistulose stems and branches. The tubular character of the stem 

 and branches is probably caused by the activity of a Crustacean, 



1 Zool. Am. xxix. 1905, p. 263. 



