CORALS. 



123 



nJi 



A genus called Isis is closely allied in many respects to CoralUum, and approaches 

 it very intimately in the great hardness of the axis. While portions of this axis are as 

 hard as that of GoraUium, the stem is not continuous, but is formed of hard and soft 

 articulations, alternating with each other. The hard joints are securely bound together 

 by softer and more flexible articulations, permitting a slight bending of the axis. The 

 IsiD^, including Isis, Mopsea, and one or two allied genera, are often used for orna- 

 mentation, but no considerable traflic with them has taken place. Tsis flexibilis, which 

 extends from the latitudes of the Caribbean Islands to the coast of Norway, is 

 one of the most graceful of this family. It is sometimes found in deep water, often in 

 the profound depths of the ocean. 



There are many genera allied to Isis, some of which are found in deep seas, which 

 present most interesting connecting features between the Isid^ and the true sea-fans 

 and sea whips. One of the most interesting of these is a beautiful ochre-colored coral 

 called Mditeea. The branches of Melitcea, like those of Isis, are composed of alter- 

 nate stony and soft joints, of which the size of the latter are relatively much ■ larger 

 than the former, which appear as bead-like expansions. M. ochracea is reddish yel- 

 low in color, and has the branching habit of the majority of the true sea--fans. It is 

 found in the Pacific and Indian oceans, many specimens bearing Singapore as the 

 locality from which they were taken. It is of considerable size, and seems to connect 

 structurally the family of 

 Isidae with the true sea^ 

 fans. 



Of the many aberrant 

 genera of Halcyonoida, 

 the genus Tubipora or 

 the organ-pipe coral, the 

 type of the family Tubi- 

 POEiD^, departs the widest 

 in general appearance from 

 that of the majority of Hal- 

 cyonoids. In this genus 

 we find no radiating par- 

 titions of hard secretion as 

 ■ in most corals, but instead, 

 a number of tubes arranged 

 side by side separated from 

 each other by a slight space 

 and bound together by hor- 

 izontal fioors. In these 



tubes live the tubipore coral, and to them it owes its suggestive name. The color is a 

 deep red, and the coral community often reaches a considerable size. It is, however, 

 very fragile, and easily crumbles under the action of the waves, presenting a great 

 contrast to the harder species of Corallium, Isis, and Mopsea. 



The sea-pens, Pennatulid^, embrace a few most interesting forms of Halcyonoida. 

 In Pennatula rubrum, the likeness to a quill-pen is very close. In this coral a central 

 axis extends from one end to the other of the body, inside a sheath from one-third of the 

 length of which there hangs^ on either side, opposite each other, rows of leaf-like disks 

 supported by calcareous spicules. Upon the faces and edges, more especially in the 



'J Mia 



Fig. 119. — Tubipora, organ-pipe coral, natural size. 



