36 THE ANTHOZOA 



corallum. Both calices and coenenchymal tubules are closed below by 

 transverse calcareous partitions or tabulae. The walls of the calices and 

 coenenchymal tubules are not separate and independent, but the calcareous 

 lamellae forming the walls of one tubule enter into the composition of 

 the walls of adjacent tubules, and the calyx walls and the pseudosepta are 

 formed by the walls of adjacent coenenchymal tubules. The colony consists 

 of zooids and solenia. The zooids exhibit a proximal moiety imbedded in the 

 calyx and a distal moiety which can be invaginated within the calicine 

 portion. Solenia are given off radially from the level where these two 

 regions pass into one another, and anastomose with one another to form a 

 more or less regular superficial network, which covers the surface of the 

 corallum. From the nodes of the network blind solenial downgrowths pro- 

 ject vertically into the coenenchyme,each occupying a coenenchymal tubule. 



The Coenothecalia are represented by a single living genus Hsliopora, 

 but the group was more largely represented in Palaeozoic times. Helio- 

 lites from the Silurian and Devonian is closely allied to Heliopora. The 

 presence of septiform radial lamellae in the calycles was long regarded as 

 a reason for placing Heliopora and Heliolites among the Zoantharia, but 

 Moseley (80) demonstrated the typical Alcyonarian structure of the 

 zooids of Heliopora, and subsequent investigations have shown that this 

 genus, with others which have a similar structure of corallum, must be 

 placed in a separate branch of the Alcyonaria. For details of the 

 anatomy of Heliopora the reader is referred to Moseley's memoir, and to 

 Bourne (9). 



Fig. XVIII. 2 shows the relations of the soft parts of the Helioporid 

 colony, and 5 shows how the walls of each coenenchymal tubule are 

 formed of twelve pieces common to that and the six adjacent tubules, the 

 calyx being formed by the arrest in growth of a group of seven central 

 tubules and the partial arrest of twelve peripheral tubules, the walls 

 of which give rise to the pseudosepta. The most remarkable features in 

 Heliopora, in addition to the laminar calcareous corallum, are the limita- 

 tion of the solenial outgrowths to the middle region of the zooid, and the 

 formation of vertical tubular down-growths from the solenial meshwork, 

 forming the so-called coenenchymal tubules. These were originally con- 

 sidered to be extremely degenerate siphonozooids, but they have no traces 

 of zooidal structure, and must rather be considered to be a specialised part 

 of the solenial system, associated with the peculiar form of the corallum. 



FAMILY 1. HELIOPORIDAE. Colonies forming broad, upright, lobed, 

 or digitate masses flattened from side to side, of a blue colour. Calices 

 with (usually) fifteen pseudosepta. The coenenchymal tubules do not 

 branch, but new tubules are intercalated between those previously 

 existing. Genus Heliopora, Pallas. From tropical seas in shallow 

 water. FAMILY 2. HELIOLITIDAE. Colonies forming spheroidal masses, 

 rarely lobate. Calices with twelve pseudosepta. Coenenchymal tubules 

 more or less regularly hexagonal. Coenenchymal tubes branch dicho- 

 tomously. Genera Heliolites, Dana. From the Lower and Upper Silurian, 

 and the Devonian. Plasmopora, M. Edw. and Haime. Silurian. Propora, 

 M. Edw. and Haime. Upper Silurian. Lyellia, Edw. and Haime. Upper 

 Silurian. FAMILY 3. THECIDAE. Colonies forming laminar expansions. 



