124 Fossil Corals, — Lower Silujian RocJcs o/' Canada. 



Genus Columnaria, (Goldfuss.) 



A very abundant family of fossil corals have a honey-combed structure, 

 consisting of a great number of angular tubes gTOwing together, each tube being 

 the cup or cell of a single polyp. The Astrceashewn in figure 2 is one of those 

 composite forms, and when dead is covered with numerous star-like openings. 

 The rays of the stars in each of those tubes of the Astrcea correspond to the 

 lamellae of the genus Streptelasma. If we could imagine a number of these 

 latter crowded together in one mass, they w^ould constitute a star covered 

 dome, something like the Astrcea. In the Lower Silurian rocks one of the 

 most common of the honey-combed corals is the columnaria alveolata. llie 

 following is a description of the genus compiled from several authors. 



Generic Characters. — Corallum forming larije masses, often of a 

 hemispheric form, cells, polygonal, radiating lamellae, rudimentary, or but 

 little developed ; transverse, diaphragms, horizontal, and nmnerous. 



The generic name is from the Latin, [Columna,) a column having 

 allusion to the numerous column-shaped tubes of which the masses of the 

 coral are composed. The transverse diaphragms are the little plates or floors 

 which extend across the tubes, dividing each into so many stories, one above 

 the other. There is one species of this genus known in Canada, and it is 

 verv common in some localities of the Black Eiver Limestone. It is the 

 following : 



Columnaria alveolata, (Goldfuss.) 



This species is thus described by Professor Hall : — " A hemispherical 

 or irregularly massive coral, consisting of radiating parallel or diverging 

 tubes ; tubes hexagonal, (or varying from 5 to 7 sided,) striated longitu- 

 dinally, crossed by dissepiments, (diaphragms,) with vertical radiating 

 lamellae ; no communicating pores. 



^ -.—'■■.■"- ..^ 



iav-^>V?5^(P^>'^r^-" -. ■ -, . ,'y^J ^ta.' '•'■^-y--'''.^■"•--- 



Fig. 9. Fig. 10. 



Fig. 9. — Is a small mass of [Columnaria alveolata,) shewing the honey- 

 combed appearance of the exterior of the fossil. 



Fig. 10. — Shews the portion of the surface of a mass ivhich has been 

 split open in the direction of the length of the tubes. Each 

 tube is seen to be divided into a number of chambers by the 

 transverse diaphragms. 



When the tubes of this coral are well preserved and empty, the interior 

 Ls seen to be striated the whole length of the tube, the elevated lines being 

 the rudiments of radiating lamellae. The coral is sometimes seen in masses 

 three feet in diameter, and when these are split open in a direction from the 

 top to the bottom, the tubes are seen to radiate from a narrow space in the 



