HAICTONOIDS. 



19 



Pig. 20. 



one fifth the height of the animal at its greatest extension. This 

 lime deposit does not, however, fill 

 the chamber for its whole width, but 

 rises as a thin waU in its centre. (See 

 Figs. 16, 17.) Thus between all the 

 soft partitions, in the middle of the 

 chambers which separate them, low 

 lime-stone walls are gradually built 

 up, uniting in a solid column in the 

 centre. These walls run parallel 

 with the soft partitions, although 

 they do not rise to the same height, 

 and they form the radiating lines like stiff lamellae, so conspicu- 

 ous when aU the soft parts of the body are drawn in. The mouth 

 of the Astrangia is oval, and the partitions spread in a fkn-shaped 

 way, being somewhat shorter at one side of the animal than on 

 the other. The partitions extend beyond the solid waU which 

 unites them at the periphery, in consequence of which, this wall 

 is marked by Mnt vertical ribs. 



HALCYONOIDS. 



Boilcyoniwm, (Hdcyonium cameum Ao.) 



We come now to the Halcyonoids, represented in our waters 

 by the Halcyonium (Fig. 22). In the Halcyonoids, the 

 highest group of Polyps, the tentacles reach their greatest 

 liroitation, which, as above mentioned, is found to be a mark 

 of superiority, and, connected with other struc- 

 tural features, places them at the head of their 

 class. The number of tentacles throughout this 

 group is always eight. They are very compli- 

 cated (Fig. 21), in comparison with the tenta- 

 cles of the lower orders, being deeply lobed, , 



Kg. a. 



rig. 20. Limestone parts of an individual of Astrangia ; magnifled. 

 Pig. 21. Single iodividual of Halcyonium seen from abovej magnified. 



