346 COELENTERATA ANTHOZOA chap. 



There is very strong reason to believe that certain fossil 

 corals were closely related to Heliopora ; that Heliopora is in 

 fact the solitary survivor of a group of Alcyonarian corals that 

 in past times was well represented on the reefs, both in numbers 

 and in species. The evidence is not so convincing that other 

 fossil corals are closely related to Heliopora, and their true 

 zoological position may remain a matter for surmise. The order 

 may be classified as follows : — 



Fam. 1. Heliolitidae.^ — Coenothecalia with regular, well- 

 developed septa, generally twelve in number, in each calicle. 



Heliolites, Dana, Silurian and Devonian. Cosmiolithus, Lind- 

 strom, Upper Silurian. Proheliolites, Klaer, Lower Silurian. 

 Plasmopora, Edwards and Haime, Upper Silurian. Proiwra, 

 E. and H., Upper Silurian. Gamptolithus, Lindstrom, Upper 

 Silurian. Diplo'epora, Quenst, Upper Silurian. Pycnolithus, 

 Lindstrom, Upper Silurian. 



Fam. 2. Helioporidae." — Coenothecalia with small irregularly 

 arranged coenosarcal coeca, and a variable number of septa or 

 septal ridges. Helio2wra, de Blainville, recent. Eocene and Upper 

 Cretaceous. Polytremacis, d'Orbigny, Eocene and Upper Cretaceous. 

 Octotremacis, Gregory, Miocene. 



The family Coccoseridae is regarded by Lindstrom as a 

 sub-family of the Heliolitidae, and the families Thecidae and 

 Chaetetidae are probably closely related to the Helioporidae. 



Order III. Alcyonacea. 



This order contains a large number of genera of great variety 

 of form. The only characters which unite the different genera 

 are that the body-walls of some groups of zooids, or of all the 

 zooids, are fused together to form a common coenenchym pene- 

 trated by the coenosarcal canals, and that the spicules do not 

 fuse to form a solid calcareous, or horny and calcareous, axial 

 skeletal support. 



The affinities with the order Stolonifera are clearly seen in 

 the genera Xenia and Telesto. Some species of Xenia form 

 flattened or domed colonies attached to stones or corals, with 

 non- retractile anthocodiae and body -walls united for only a 



1 G. Lindstrom, Handl. k. Svensl: Vet. Akad. xxxii. 1S99. 

 - J. W. Gregory, Proc. Roy. Soc. Ixvi. 1899, p. 291. 



